PAPERS ON ZOOLOGY 



289 



There lias been a general acceptance of the view that 

 the spines surrounding the orifice of the male function 

 during copulation, probably as a means of attaching the 

 male to the female. Advocates of this view have failed 

 to recall the fact that the copulatoiy apparatus of the 



Corynosoma constrictum FanC 



Fig. 10. Young female showing spines around' genital orifice. 

 Fig. 11. Gravid female showing copulatory cap which is attached 

 at time of copulation. 



male acanthocephalan must be everted from a position 

 far within the body before it can be brought into position 

 for use. When the copulatory bursa containing the cir- 

 rus is extruded during copulation the genital spines 

 could not serve for attachment to the female (Fig. 9) 

 because they lie behind the bursa and are completely 

 covered by it. 



COXCLUSIOXS 



Many theories have been advanced to explain the ori- 

 gin and development of sexual dimorphism. Of these 

 natural selection and sexual selection have probably 

 been most prominently advocated. J. T. Cunningham 

 (1900) has advanced a modified form of inheritance of 

 acquired characteristics as explanation. According to 

 his ^-iew organs or structures used directly or indi- 

 rectly in the reproductive process become modified 

 through function. Thus a tendency toward modification 

 in such structures is passed from generation to gener- 



