164 ILLINOIS BIOLOGICAL MONOGRAPHS [164 



field is limited by the vitellaria, the anterior margin of the segment and 

 the ovaries. There is no median zone free from them except where 

 they are pushed aside by the developing uterus. As the uterus con- 

 tinues to develop the testes are pushed well into the lateral fields. 



The vagina (Fig. 176) which has a large lumen runs to the middle 

 of the proglottid in a more or less sinuous course, then bends and passes 

 directly back to the posterior end of the segment. In proglottids with 

 developed uterus the vagina is pushed somewhat from the median line 

 and, it seems, always toward the side on which it opens. The ovary is 

 posterior, is bilobed, and the lobes are limited laterally by the vitellaria. 

 In the end-proglottid the lobes of the ovary are bent together. The 

 vitellaria are follicular and lateral. On the porose side the vitellaria is 

 divided into two parts connected by small follicles which lie dorsal and 

 ventral to the genital passages. The uterus (Figs. 175, 176) is a median 

 tube reaching to the anterior end of the proglottid from which arise 

 many (10-12 in drawing) lateral outpocketings. These are separated 

 when fully developed by thin tissue-layers. The eggs are pear-shaped, 

 circular in cross-section, 0.016 mm. in diameter and 0.029 mm. long. 



Despite the fact that Klaptocz found an apparently intergrading 

 series between the types of head mentioned by him it seems to the 

 writer that there is a possibility of his having confused two forms of 

 very similar appearance. The writer in the present work on Proteo- 

 cephalus pcrplexits and P. ambloplitis found considerable difficulty in 

 distinguishing the heads. And in certain respects the structure of the 

 internal organs of the proglottids was remarkably similar. So too it 

 was found to be difficult to distinguish the proglottids of P. perplexus 

 and P. singularis. This was made especially difficult when both species 

 occurred in a specimen of Lepisosteus platostomus. The fact that this 

 species seems to occur in two such widely separated families of fish is 

 a further intimation that two species of parasite are here included 

 under the one name. Material from the two hosts should be carefully 

 reworked. 



