792 SUMMARY OF CURRENT RESEARCHES RELATING TO 



placed on the canal, but not at its extremity. Ankyroderma appears to 

 be transitional between the Synaptidse and the Mulpadidse. 



Histology of Digestive Canal of Holothuria.* — E. Jourdan finds, 

 in Holothuria tubulosa, that the cells of the epithelial or peritoneal 

 layer are of two kinds ; simple endothelial cells arranged in a single 

 layer, cylindrical in form and often ciliated, while the others are of 

 the type of mucous cells. The muscular layer is formed by circular 

 and by longitudinal fibres, the former being continuous and regular, 

 ■while the latter are most numerous in the anterior region of the tract, 

 while, again, they are placed internally to the circular muscles 

 anteriorly, and are external to them posteriorly. A number of 

 lacunae are to be found in the connective layer. The cells of the in- 

 ternal epithelial layer differ remarkably in different regions ; while 

 they are at first excessively long, and have the form of delicate fibrils, 

 they are, further from the mouth, distinctly cylindrical. The glan- 

 dular cells with granular contents are ovoid or spherical and appear to 

 be confined to the more anterior regions, while the so-called mucous 

 glandular cells are more widely distributed, with, however, consider- 

 able variations in their form, size, and number ; in the more posterior 

 portions of the intestine they may be compared to the mucous cells of 

 the Vertebrata. 



Ccelenterata. 



Studies on Coelenterates.j — Dr. 0. Hamann finds that the cnido- 

 cells are interstitial cells which have developed an urticating capsule in 

 their interior and have then passed from the lower to the more super- 

 ficial layer of the ectoderm ; it may be shown by the presence of the 

 nucleus after the formation of the capsule that this last owes its origin 

 to the protoplasm of the cell. At the same time the cell is capable 

 of producing a process which becomes connected with the supporting 

 lamella, and has many if not all of its characters ; this process is not 

 a mode of communication from the exterior to the interior of the 

 organism, but only a supporting fibre ; if this view be the correct one 

 it is clear that the cnido-cells cannot be looked upon as having a sensory 

 function, but rather as being partly defensive and partly offensive. 



In discussing the pseudopodioid cells of Hydra it is remarked 

 that, if we examine the region of attachment we find that the ecto- 

 dermal cells are here different from what they are in other parts of 

 the body ; cylindrical in form, their contents are not clear but finely 

 granular ; if separated, after maceration, they are seen to have only 

 one and not two of the so-called muscular fibrils ; and if carefully 

 studied in the living specimen they may be seen to be capable of 

 excreting mucus ; if examined, when the animal is in movement they 

 may be shown to protrude pseudopodia. No interstitial cells or cnido- 

 cells are to be found in this region. The apparent absence of pseudo- 

 podioid cells in all other Coelenterates leads the author to believe 

 that Hydra is really a form standing very close to the ancestor of the 

 Hydroid Polyps ; though he recognizes the possibility of the objection 

 being raised that Hydra has lost its skeleton in fresh water. 



* Compt.es Kenclus, xcv. (1882) pp. 565-6. 



t Jeuaisch. Zeitschr. f. Naturwiss., xv. (18S2) pp. 545-57 (2 pis.). 



