296 J. H. ASHWOETH. 



below the lower end of the stomodseum. They are not present 

 in the mesenteries of the free portion of the polyp, but in the 

 portion enclosed in the stem. They are therefore in the 

 position in which the genital products of the adult polyps are 

 most numerous (see p. 263, and fig. 8). 



c. They agree in size and are similar (especially their large 

 vesicular nuclei) in appearance to the primitive genital cells of 

 the adult. 



Fig. 36 shows a section through a ventral mesentery of a 

 slightly older polyp (No. V in table, p. 284). The genital 

 cells are still more clearly marked than in the preceding polyp, 

 and, as shown in the figure, are readily distinguished by their 

 large vesicular nuclei. Many of them have already taken up 

 their position in the mesogloea. 



On comparing the polyp '8 mm. long with one about 

 two thirds its size ('56 mm. long) it is seen that during the 

 period in which the elongation of "24 mm. was accomplished, 

 many important adult structures were acquired, viz. the 

 first indication of pinnules on the tentacles, the open mouth, 

 the siphonoglyph, the goblet-cells in the stomodseum, the 

 dorsal mesenterial filaments, and the primitive genital cells. 

 A polyp which has reached this stage of development would 

 probably be quite capable of supporting itself, as, by means of 

 its siphonoglyph and dorsal mesenterial filaments, it would be 

 able to create the currents necessary for its nutrition and for 

 keeping up the circulation of liquid in the ccelenteron. 



In a polyp "95 mm. long (V in table, p. 284) the first two 

 pinnules are distinguishable upon each tentacle. The stomo- 

 daeum is "6 mm. long, and the siphonoglyph extends along the 

 ventral side of the lower, '34 mm. The lips of the stomodseum 

 are widely open below. Flagella-bearing cells are much more 

 numerous in this polyp than in any of the young polyps 

 previously described. They are fewer in number in the upper 

 part of the coelenteron than in the deeper portions. Their 

 flagella are still short, not exceeding 30 [x in length (fig. 36, 

 G. F.). 



A polyp 1 mm. long (VI in table) is seen in section in PI. 



