Cited by M. Greenwood, 'On Digestion in Hydra, with some Observations on the Structure of the Endoderm', Journal of Physiology 9 (5-6) (1888), pp. 317-344.
Description:

Explanation of Plate VI (figs. 1-10):

'Fig. 1. Vertical section through body-wall of digesting Hydra, early stage of digestion.

Fig. 2. Vertical section taken later in digestion, showing vacuolar deposit of nutriment in large endoderin cells and loss of the spherules of gland cells.

Fig. 3. Vertical section taken at the end of an act of digestion, showing emptied gland cells, and fully formed nutritive spheres.

Fig. 4. Group of cells teased from endoderm in hunger. To show connections of pigment in vacuolate endoderm cells, and persistence of secretory spherules. Oc. 3, Obj. F. Zeiss

Fig. 5. Cells isolated by teasing.

a. b. c. d. gland cells in different stages of activity

a. b. d. drawn with Oc. 3, Obj. D. Zeiss.

c. drawn with Oc. 3, Obj. F. Zeiss.

A. Absorptive endoderm cell from the animal in which b. was found. Oc. 3, Obj. D. Zeiss. 

Fig. 6. Vertical section through foot cells of Hydra; digestive endoderni of same animal is drawn at Fig. 2.

Fig. 7. Vertical section through lip showing modified endoderm cells.

Fig. 8. Vertical section throuigh modified ectoderm of sucker.

Fig. 9. Pigment of Hydra fusca as seen in specimens teased from diluted Flemming's fluid.

Fig. 10. Vertical section through body-wall of Hydra viridis to show simulated "villus," presence of gland cells, and coexistence of nutritive spheres and chloroplastids.

Except where otherwise specified the magnification throughout is that effected by combination of Oc. 3, Obj. D. Zeiss.' (343-344)

 

Figs. 1-6 in text:

'Vacuolate endoderm cells. In the larger endoderm cells (Plate VI. E figs. 1, 2, 3, 4, 6) one may distinguish structural features which are relatively permanent, and others which slowly come and go. Thus cell substance, a nucleus with at least one well-marked nucleolus, and fluid forming a vacuole or vacuoles are discernible whatever the condition of the animal examined; they are not however always obvious, for changing circumstances bring one or another into relative prominenice. Among the temporary constituents of the cell we may distinguish the brown or black pigment, and certain spherical deposits of proteid, probably of the nature of reserve material.' (318)

 

Figs. 1-2 in text:

'I must confirm the account of the act of feeding which Hartog [note: 'M. Hartog. Quart. Journ. Mic. Sci. Vol. xx. 1880.'] gives in his note " On the mode in which Hydra swallows its prey," and repeat that while the tentacles may arrest a moving animal and discharge their nematocysts into its body they are never used for tucking the prey into the interior of the Hydra, but remain extended and waving freely during its enclosure (cp. Pl. VII. figs. 1, 2). The lip, to use Hartog's expression, is drawn or pushed over food much as a glove may be advanced over the finger.' (339)

 

Figs. 1-3 and 10 in text:

'When the endoderm is examined at the beginning of a digestive period the glands still show plainly (fig. 1, g, Pl. VI.), and after food bas been within the Hydra for as long a time as two or three hours the spherules may be quite evident; the onset of absorption however, marked by initial vacuolar deposits and final separation of solid matter in the absorbing cells, appears to be bound up with solution of the spherules which we are thus impelled to call secretory. (Fig. 2.) At anyrate at the end of a digestive period the gland cells are so inconspicuous that I was at one time inclined to the view that they are lost bodily as secretion goes on; and though careful searching, revealing them, seems to negative such a suggestion, it shows them empty and shrunken, or at most holding fragmentary contents in fluid surroundings. (Figs. 3, 10.)' (334)

'The mobility of the Hydra's body is very great, and the vacuolate elements of the endoderm are capable of considerable change of form and varying disposition of their substance. They lie side by side, cylindrical or cubical in shape when the whole animal is extended, or distended as it may be at times by food (fig. 1, Pl. VI.); they are commna shaped in general contraction of the body, bulging apically and becoming greatly attenuated at their attached bases. They are even sometimes thrown up into simulated villi (Pl. VI. fig. 10), after the fashion of the mucous membrane of the frog's intestine. But the gland cells, destitute of vacuole, can undergo less alteration of form and shrink and expand but little. Unless borne up on the side of a "villous" formation therefore by great attenuation of their basal processes, they lie far from the surface, when as in the contracted state of Hydra, the endoderm generally is deep; extension over prey on the other hand brings all the cells present to a level. (Cp. figs. 2 and 3 with fig. 1.)' (338)

 

Fig. 1 in text:

'The Cell substance [of the vacuolate endoderm cells of the Hydra] forms the external layer of the cell; it is somewhat massed towards the attached base, and more so at the free border which I will call the apex, here giving rise to a fairly conspicuous semilunar accumulation. (Fig. 1, Plate VI.) Bridles of cell substance, such as commonly pass from the perinuclear protoplasm of a vegetable cell to that layer of substance which lines the wall, are rare in the endoderm of Hydra, for the nucleus is excentric in position and projects inward from one lateral wall, but the apical mass of protoplasm in its inner part may be honeycombed by small vacuoles (fig. 1, V). It is in this apical mass that the slight power of amoeboid movement possessed by the cells becomes manifest, and in specimens examined in the fresh state it is exhibited by the formation of blunt hyaline projections which arise fromn the apex of each cell and are never probably more than one-fourth of the depth of the aggregation of substance from which they spring.' (318-319)

Hitherto, 'it has proved difficult to avoid reference to the fluid which constantly occupies the middle region of each large cell, and forms the third of those cell constituents which I regard as permanent. This fluid varies considerably in amount and not a little in disposition. Typically it exists as a large central vacuole unbroken by bridles of protoplasm, while the nucleus and any other differentiated solid matter which may be present project into it from the base, side or apex of the cell, and are held in place by an investing sheet of protoplasm. Sometimes (fig. 1, V, Pl. VI.) however fluid is gathered by the apical cell substance into tiny vacuoles in itself; this is a characteristic appearance during the early stages of digestive activity, and it is at a somewhat later time, that is to say, after digestive activity has been marked that the total quantitv of fluid present is the least.' (320-321)

 

Figs. 2-7 in text:

'Nutritive spheres. These are figured at n in figs. 2, 3, 5, 6, 7, Pl. VI. and have been previously described, though with marked brevity, by all writers on the structure of Hydra.' (321)

 

Figs. 2-3 in text:

'it would seem that the turbid spheres are in process of deposition, those with homogeneous substance being perfect. I imagine that the deposition takes place in the apices of the cells (fig. 2, v, P1. VI.), and the spheres as they are sbaped come to occupy a more basal place; when digestion has ceased and the process of formation is no longer going on, then no turbid, unelaborated spheres are to be recognised but all are homogeneous (fig. 3).' (324)

 

Fig. 2 in text:

'Two points in the disposition of the protoplasm.of an endoderm cell remain, and demand notice. In the first place part of the substance of the lateral wall may bulge internally, formiing spherical projections shaped after the fashion of those which hold the nucleus in place, and these at times enclose solid bodies,-the constituents of the cell to which I have already alluded as relatively temporary in their nature, and which I shall presently describe in detail. In the second place such spherical bulgings may exist and hold no solid matter but apparently a fluid; in this case they are apical rather than lateral in origin and project down into the main vacuole. (Fig. 2, v, Pl. VI.)' (319-320)

 

Figs. 3-4 in text:

'I have noticed that in the endoderm cells of a well-fed Hydra the pigment is generally difficult to distinguish, though sometimes it is to be found not now as normally at the apex of the cell, but moved down one side wall. In the endoderm of a fasting animal it is most conspicuous, partly because here the cells are comparatively empty and but few nutritive spheres strike the eye, but also I think because it is actually great in quantity (cf. figs. 3 and 4, PI. VI.). I do not forget that Nussbaum [note: 'M. Nussbaum. Loc. cit.'] describes the tint of Hydra fusca as paling in long hunger, and that this at first sight appears contradictory of the statement just made. The contradiction is, I think, only apparent, for it must be remembered that long hunger means the disappearance of many opaque bodies, - the proteid spheres, and that possibly the highly vacuolate, partially empty cells are more transparent than are those loaded with reserve material.' (330)

 

Figs. 3 and 6 in text:

'The nucleus is found most commonly in the lowest third of each cell bulging into the vacuole, and is bounded internally by a thin pellicle of protoplasm; occasionally however it may lie quite near the base, or again may be displaced apically. (Figs. 3, 6, nuc. Pl. VI.) The changes of position which come about in the nucleus and in any other solid bodies which may happen to be present in the endoderm appear comparable to the movements of chlorophyll corpuscles in the protoplasm of a plant cell under the stimulative actioni of considerable changes in illumrination.' (320)

 

Fig. 3 in text:

'Ray Lankester in his paper on the Intracellular Digestion of Limnocodium refers to this account, and regards the gland cells and goblet cells of Claus as young and older stages of the same structures. He compares them with certain cells found characteristically in the oral third of the gastric tube of Limnocodiuim; these are large, clear, nucleated bodies which, together with smaller young cells, are surrounded by some horny or gelatinous intercellular substance. A complete description of the young cells is not given, nor are there details of the stages through which one form grows into the other, but the appearance of Pl. IX. fig. 3, indicates that the young cells are denser and stain more deeply than do the adult "glands" into which they grow.' (337)

 

Fig. 5 in text:

'The gland cells are especially conspicuous when almost filled with homogeneous spherules; these, between the nucleus and the apex, are so abundant as to hide the protoplasm which holds them, and, since the nucleus lies rather near the base of the cell, it is but a small portion of cell substance that can be distinguished and observed. This is dense and stains deeply, and passes back apparently without marked histological change into the internal basal process. This process becomes so delicate that it is but rarely either in sections or teased preparations actually to be traced to the supporting lamella. (Fig. 5, a Pl. VI.) At other times the spherules are present, but are much reduced in size and often of angular shape, and each has fluid suirroundings (Fig. 5, b); while after complete loss of formed contents two distinct appearances may be possibly presented by the cell. The first is that of a reticulum, the meshes of the network being large, while its separating bars are thin; here as before the protoplasm lying basally of the nucleus is unmodified. The last is no longer that of a honey-combed mass of substance; rather the gland cell is dense and irregularly furrowed and, ceteris paribus, smaller now than at any time. (Fig. 5, d.) Thus we have apparently a storage of matter in the form of spherules, and at times a loss of these spherules through the solvent action of fluid poured round them, probably by protoplasmic energy.' (333)

 

Figs. 6-7 in text:

'I have said above that certain structural modifications other than those yet noticed remain, and demand brief consideration. The first of these is found in the foot and tentacles. In both regions the vacuoles of the large cells are very conspicuous (Fig. 6, Pl. VI.) and the cell substance is relatively scanty. Pigment groups and nutritive spheres occur, the pigment being indistinguishable in amount and disposition from that of the gastric tube, while the nutritive spheres are as a rule smaller than those found in the main part of the endoderm. In the lip certain cells constantly occur which I have represented diagrammatically in Fig. 7. Their substance is dense, and in the fresh state filled in its outer part with little shining granules which break down in acids and alkalis.' (338)

 

Fig. 8 in text:

'The endoderm of the sucker of Hydra has been described by Jickeli [note: 'C. F. Jickeli. Loc. cit.'] as made up of a "second kind of gland cell." I have not been able to find any qualitative difference between these and the rest of the absorptive endoderm. There is, truly, marked diminution in size and the vacuoles are less conspicuous, still the cell substance is loose and not definitely structured, and pigment is commonly present. It is in the subjacent ectoderm figured at Plate VI. fig. 8, that obvious modification occurs, and here the structure recalls that found in the lip and already described.' (338-339)

 

Fig. 9 in text:

'Sometimes specimens of Hydra are found in which the diffuse pigment is conspicuous, while others are almost entirely tinted by well-defined lumps of pale or colourless substance bearing dark, angular, perhaps crystalline particles [note: 'Cf. Howes. Atlas of Biology, P1. xvii. figs. xv. xvi.'] (fig. 9, a, b, c, P1. VI.).' (328)

'I have said that fragments of proteid reacting like the nutritive spheres may lie at the apex of an endoderm cell during hunger in marked fluid surroundings, and fig. 9, Pl. VI. represerits an instance of the considerable vacuole in which pigmented proteid is at times found.' (331)