HISTOLOGY OF HYDRA FUSCA. 
221 
ternij and quite sufficient to speak of ectoderm cell with con- 
tractile process. 
The interstitial tissue, discovered by Kleinenburg, is quite 
readily made out in all parts of the body except the proximal 
end, where nematocysts are also absent. It is not mentioned by 
KorotneflP, and, indeed, its existence would be impossible if the 
large ectoderm cells had the shape described by him. 
I have found no interstitial cells in the tentacles ; this would 
seem to show that the ordinary ectoderm cells may also be the 
mother cells of the nematocysts. The ectoderm cells of the 
tentacles also differ from those of the body from the fact that 
their nuclei are non-nucleolate, resembling, indeed, the nucleoli 
of the body-cells, rather than their nuclei, 
2. The Supjiorting Lamella . — This structure is clearly distin- 
guished by Schulze and by Korotneff, the latter of whom, how- 
ever, figures it^ as almost equal in thickness to the diameter of 
an ectoderm cell ! Kleinenberg states that the muscular pro- 
cesses are imbedded in a structureless cementing substance, and 
that this, continued beyond the muscular layer on the endoderm 
side, forms a layer — the Stiitzlamelle^^ of Eeichert — which can 
sometimes be obtained as a separate structure. 
This description by no means expresses the distinctness of the 
supporting lamella. In specimens preserved in osmic acid or 
ammonium bichromate, without subsequent treatment with alcohol, 
it is easy, by teasing with fine needles, to detach shreds of con- 
siderable extent, more or less free from attached muscular fibrils 
and from cells of the interstitial tissue. 
3. The Endoderm . — The ciliation of the endoderm is a question 
about which there has been a good deal of discussion. iSchluze 
figures a single fiagellum to each cell, as seen in optical section 
of the tentacle. Kleinenberg was unable to demonstrate the 
existence of fiagella in the uninjured animal, or in preserved 
specimens, but in transverse sections of the living animal he ob- 
served one or two cilia in connection with more or fewer of the 
cells, and noticed that they were not fixed structures, but were 
occasionally retracted, and then protruded again, the cells at the 
same time sending out pseudopodial processes. 
It is quite easy to confirm this observation ; the slow lashing 
movement of the fiagelliform cilia their continual disappearance 
and reappearance in fresh places can be made out without diffi- 
culty. But the best notion of the characters and relation of the 
cilia is obtained by teasing out, or, still better, by cutting thin 
sections of osmic acid specimens. Such preparations quite lead 
one to think that the endoderm is ciliated throughout ; in the 
sections particularly cell after cell is seen bearing one, two, pr 
^ Loc. cit., pi, 15 , fig. 8. 
