294 J. H. ASHWORTH. 



size, and the four intermediate ones somewhat smaller. Does 

 this indicate the order of development of the tentacles ? This 

 bud resembles the preceding one in all essential particulars. 



4. There are several important new structures noticeable in 

 a young polyp '8 mm. in length (No. IV in table, p. 284). 

 The tentacles are very slightly indented a short distance from 

 the tip ; this is the first indication of the formation of pin- 

 nules upon the tentacles. 



The stomodseura is 'S/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 distin- 

 guishable 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 stomodaeum contain a large cavity, and 

 are similar to the goblet-cells described in the stomodseum of 

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

 the stomodaeum, and do not occur among the cells forming the 

 siphonoglyph. 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 intermesenterial 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 stomodseum. 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 fx 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 



