54 ILLINOIS BIOLOGICAL MONOGRAPHS [404 



either dorsal or dorsomedian, and Cittotaenia has them dorsal, lateral 

 or dorsomedian. Usually the dorsal duct is lateral in Anoplocephala 

 and Schizotaenia ; but in certain stages of contraction it has been ob- 

 served to be directly dorsal in both genera. In Andrya the dorsal duct 

 is lateral in all cases observed. In the scolex of all species of Andrya 

 and Anoplocephala which were observed however, the dorsal duct is 

 dorsal while in Schizotaenia anoplocephaloides it is lateral in the scolex. 

 It would appear therefore that little evidence as to relationship is 

 provided by the excretory ducts. 



THE EVOLUTION OF THE ANOPLOCEPHALIDAE 



The following arguments favor the conclusion that Andrya ap- 

 proaches most closely of all the genera to the ancestral type of the 

 Anoplocephalidae. 



1. In Andrya the ovary is either median, or very close to the 

 median line, and none of the female glands are far from the median 

 line. 



2. In Andrya the vagina and vaginal pore are directly posterior 

 to the cirrus pouch. 



3. In Andrya is found the most generalized distribution of testes, 

 with the possible exception of Aporina. 



4. In the generalized species of Andrya is found a primitive, un- 

 modified vas deferens, which character is found in no other genus except 

 Aporina. 



5. In Andrya is found the most genuine and least modified reticu- 

 late uterus. 



6. In Andrya, the uterus in anlage, crosses the excretory duct 

 ventrally. 



As characters of more doubtful value, the following may be noted. 



1. The pyriform body is simple (no pyriform body in Aporina). 



2. The vesicula seminalis is, in the most generalized species, a 

 simple, globular expansion. 



3. The genital pores are in some species irregularly alternate. 

 As specialized characters of Andrya I can see but one ; the genital 



pores are either dextral or tend towards dextrality, whereas one would 

 expect the ancestor of the Anoplocephalidae to have single, irregularly 

 alternating genital pores. Such a point constitutes but a slight depart- 

 ure however in the light of the different arrangements that have arisen 

 in the family; and in this regard evolution could easily reverse its 

 action. The possession of a prostate gland would seem at first to be a 

 specialized character; but this structure appears to be associated with 





