144 BULLETIN OF THE 



in situ, and have not migrated from the cniduphore tlirough the com" 

 municating canal and become incorporated into the " hepatic " cells, 

 is indicated by the fact that they are found in diftereut stages of de- 

 velopment (Fig. 14, nVcy.'). One finds first of all small ovoid areas, 

 which stain deeply ; later, one finds an elongated deeply staining central 

 streak, while the rest of the vGsicle remains colorless. This central 

 streak is the proximal part of the thread. In some cases I have seen in 

 the " hepatic " cells the larger kind of nematocyst mentioned by Alder 

 and Hancock ('55, Expl. Fam. 3, Plates 7 and 8, Fig. 16); in fact, 

 they seem to occur quite as abundantly here as in the cnidophore. 



Comparing the origin of nenaatocysts in the J^olidse and Hydra, — for 

 a knowledge of which in the latter group we are indebted among others 

 to K. C. Schneider ('90, pp. 332, 345), — the most striking diflerence is 

 that the nettle capsules in Hydra arise in the ectoderm only (so it is 

 maintained), and that those which do occur in the entoderm have not 

 been formed there, but have been devoured. In ^olis, similar capsules 

 arise in diverticula of the alimentary tract, and therefore from entoderm. 

 Secondly, the nettling capsules of Hydra are formed in indifferent cells 

 lying at the base of the ectoderm ; in ^olis they are produced in the 

 large " hepatic" cells. Finally, in Hydra only one nematocyst is formed 

 in a single cell, and this comes to occupy nearly the whole of it ; in 

 ^olis several nematocysts (Figs. 13, 14) are produced in a single cell. 



This comparison raises the question whether the so called hepatic ca3- 

 cum is properly named, — Avhether its cells have either the function of 

 storing up reserve stuff or of secreting digestive fluids. To this question 

 I can give no final answer, but it is worthy of note that the " hepatic " 

 cells of ^olis do contain numerous small granules which stain deeply in 

 heematoxylin. This is true even for the cells whicli produce nematocysts 

 (Figs. 14, 15). A comparison with sections of the hepatic coeca of Doto 

 coronata treated in the same way shows, liowever, that the "hepatic" 

 cells of ^olis are smaller and contain smaller granules than do those 

 of Doto, in which genus, of course, no nettling organs are formed. 

 From their smaller size, and the smaller size of the contained gi-anules 

 (whether these are stored food stuiT or katabolic product), I am inclined 

 to regard the hepatic function of the cells forming the wall of the coecum 

 of ^olis as less important than in Doto. 



The sum total of the nematocysts in the hepatic coecum of any ceras 

 is much greater than in the cnidophoi'e. On physiological grounds the 

 latter term is in .^i^olis applicable to the entire cujcum, and not merely 

 to its distal part. 



