PAPERS ON ZOOLOGY 287 



North American species belonging to the genus Filicollis 

 in which the males bear conspicuous body spines while 

 those of the females are very inconspicuous. 



In the genus CorA-iiosoma the cuticular spines cover the 

 anterior region of the body in both sexes. According to 

 Liihe (1911:37) the males of C. striimosum (Eud.) and 

 of C. semerme (Fors.) possess numerous strong cuticular 

 spines surrounding the genital orifice at the posterior 

 extremity in addition to these on the anterior extremity 

 of the body, but the genital spines are entirely wanting 

 in the females of the same species. This stands as the 

 only instance in literature of the presence of structures 

 in the body of one sex among acanthocephalans entirely 

 absent in the other sex. But since in C. semerme the 

 spines around the genital opening of the male are directly 

 continuous with those distributed on the remainder of 

 the body even this instance become an example of rela- 

 tive distribution of body spines rather than separation 

 of genital spines and body spines. In the original de- 

 scription of Corynosoma constrictum VanC, the writer 

 failed to discover any cuticular spines around the genital 

 orifice of the females. An abundance of specimens be- 

 longing to this species, recently received from Mr. L. B. 

 Dickey, has made it possible to re-examine this question 

 and has thrown considerable light upon the nature of 

 the dimorphic condition of the spines in at least the 

 North American species, C. constrictum. 



In the new collection mentioned above, I have discov- 

 ered that young females (Fig. 10) possess genital spines 

 closely resembling those of the male, (Figs. 7 to 9) ex- 

 cept slightly smaller in size. In later development, and 

 especially after copulation has taken place these spines 

 become less conspicuous in the female. In some in- 

 stances I have been able to observe that spines have been 

 apparently forcibly removed from the body as evidenced 

 by the frayed nature of the cuticula in the region of the 

 genital aperture. In this species, as in many other 

 acanthocephalans, a cap-like structure (Fig. 11) covers 

 the posterior extremity of the female following the act of 

 copulation. This structure, for which I propose the name 



