

224 J. H. ASHWORTH. 



very slightly indented a short distance from the tip ; this is the first 

 indication of the formation of pinnules upon the tentacles. 



The stomodseuni is - 57 mm. long, and oval in transverse section. 

 It is open throughout its whole length, thus placing the coelenteron 

 in communication with the exterior. There is now also a marked 

 ventral groove, which, however, is not distinguishable in the outer 

 third of the stomodseum. The cells of the lower two thirds of the 

 groove bear flagella, except for a very short distance near the inner 

 end. Some of the cells of the lower half of the stomodseum contain a 

 large cavity, and are similar to the goblet-cells described in the 

 stomodeeum of the adult. They are more numerous on the lateral 

 walls of the stomodeeum, and do not occur among the cells forming 

 the siphon °gly ph. The ectodermic muscles of the tentacles and the 

 retractor muscles on the mesenteries are now quite obvious. The 

 endoderm covering the mesenteries and lining the body-wall is very 

 thick in the free portion of the polyp, (as in Fig. 28), and the inter- 

 mesenterial spaces are consequently very small. The mesenteries 

 may be traced nearly to the end of the coelenteron, i.e., about 1 mm. 

 below the lower end of the stomocla3um. Flagella-bearing cells are 

 present in the middle and lower portions of the coelenteron, but the 

 flagella are still few in number and of small size, never exceeding 20 ji 

 in length. 



The most novel feature in this polyp is the presence of dorsal 

 mesenterial filaments, which may be traced more than halfway ("6 mm.) 

 down the free edge of the dorsal mesenteries. They have already 

 acquired their typical structure, i.e. each is a band of ciliated cells on 

 the somewhat thickened edge of each of the dorsal mesenteries, and 

 there is a longitudinal groove down the middle of the band, so that in 

 transverse section it is V-shaped. The filaments have a very sinuous 

 course, and are therefore cut across two or three times each in the same 

 section. These filaments are undoubtedly derived from the lower end of 

 the stomoda^um, with which they are perfectly continuous. Their cells 

 are exactly like the cells of the stomodaBum, being small and having 

 homogeneous or finely granular deeply staining protoplasm and dark 

 nuclei. Their cells differ markedly from the cells of the surrounding 

 endoderm, which are larger, have reticulate protoplasm, stain more 

 lightly, and have less distinct nuclei. 



There is another very interesting feature worthy of note in this 



