1879.] 



On the Histology of Hydra fusca. 



63 



combining Kleinenberg's and Korotneff's, and speaking of epithelio- 

 neuro-muscle cell ; but, fortunately, it is unnecessary to employ any 

 such cumbersome term, and quite sufficient to speak of ectoderm cell 

 with contractile process. 



The interstitial tissue, discovered by Kleinenberg, 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 Korotneff, 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 (fig. 5) ; 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- 

 nucleoiate, resembling indeed the nucleoli of the body cells, rather 

 than their nuclei (fig. 5). 



2. The Supporting Lamella. This structure is clearly distinguished 

 by Schulze and by Korotneff, the latter of whom, however, figures it* 

 as almost equal in thickness to the diameter of an ectoderm cell ! 

 Kleinenberg states that the muscular processes are imbedded in a 

 structureless cementing substance, and that this, continued beyond the 

 muscular layer on the endoderm side, forms a layer — the " Stiitz- 

 lamelle " of Reichert — which can sometimes be obtained as a separate 

 structure. 



This description by no means expresses the distinctness of the sup- 

 porting 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 considerable extent, 

 more or less free from attached muscular fibrils and from cells of the 

 interstitial tissue (fig. 2). 



3. The Endoderm. — The ciliation of the endoderm is a question 

 about which there has been a good deal of discussion. Schulze 

 figures a single flagellum to each cell, as seen in optical section of the 

 tentacle. Kleinenberg was unable to demonstrate the existence of 

 flagella in the uninjured animal, or in preserved specimens, but in trans- 

 verse sections of the living animal, he observed one or two cilia, in 

 connexion 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 flagelliform cilia, their continual disappearance 

 and reappearance in fresh places can be made out without difficulty. 

 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 



* Loc. cit., PI. 15, fig. 8. 



