26 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



cells (fig. 12, D). Later these gather again into the limbs of the horse- 

 shoe, which become enlarged and entirely distinct from each other 

 (F). The third change is the formation of the plug of optic cells, 



which arises by the tip of the arch of the 

 horseshoe curling over backward (fig. 12, 

 C) and later becoming the almost inde- 

 pendent mass of cells figured (E, F, and 

 pi. 2, figs. 7 and 8). For more adequate 

 description of the structure and develop- 

 ment of the ganglion and eyes of Cyclo- 

 salpa pinnata see Metcalf (1893, c). 



The neural glands are similar in the 

 solitary and aggregated forms. 



a.o. 



Fig. 13.— Cyclosalpa pinnata, SUBSPE- 

 CIES POLAE, SOLITARY FORM, DORSAL 



view. From Sigl (1912, a). 



CYCLOSALPA PINNATA, subspecies POLAE (Sigl) (1912). 



Cyclosalpa polae Sigl (1912). 



This subspecies is said by Sigl to be dis- 

 tinguished by two features : first, in the 

 solitary individuals, the fusion of body 

 muscles VI on the dorsal mid line and 

 their continuance forward as a median 

 muscle band reaching almost to the level 

 of body muscles II (fig. 13) ; and, second, 

 the long peduncle by which the aggre- 

 gated zooids are united to form the wheel 

 (fig. 14). 



In the collections of the United States National Museum submitted 

 to us are three specimens of the solitary Cyclosalpa pinnata which 

 are of the subspecies polae. One is 17 mm. long; one is 7 mm. 

 long; the third is an 

 embryo 8 mm. long, 

 in which the placenta 

 is present. None of 

 them show any peculi- 

 arity beyond the pres- 

 ence of the median 

 dorsal extension of 

 body muscles VI. In 

 the same bottle, and of 

 course from the same 

 place of collection, is fig 

 another solitary indi- 

 vidual 24 mm. long, of the usual pinnata character. There are also S 

 aggregated zooids 14 mm. long, four of them still attached together in 

 a broken wheol, and 2 aggregated zooids 1 1 mm. long, not attached. 



M+JZ 



a.c. 



14.— Cyclosalpa pinnata, subspecies polae, aggregated 

 zooid viewed from the side. From Sigl (1912, a). 



