1919] Cort: A New Distome from Rana aurora 295 



the "2-3-6" type and its derivatives may represent a character sur- 

 mounting family limits, as is suggested by the present classification 

 of the forms exhibiting this peculiarity. On the other hand an 

 increase in the number of species for which the excretory system is 

 known may make necessary fundamental rearrangements in the 

 classification. 



Development 



The character of the cercaria from which Margeana calif or rviensis 

 develops is not known from direct observations. However, some idea 

 can be given of the type of cercaria of this species from what is known 

 of the cercariae of related forms, from comparisons with the types 

 of excretory systems found in cercariae, and from the structure of 

 immature individuals. The structure of Margeana californu nsis, 

 especially as shown in immature specimens (fig. 5) agrees in the 

 relative size and position of the suckers, the character of the digestive 

 system and the position of the genital pore with the stylet cercariae. 

 The finding of the "2-6-3" type of excretory system in Cercaria 

 polyadena (Cort, 1919), a stylet cercaria of the polyadenous group, 

 strengthens this comparison. Also the cercariae of two of the species 

 with the "2-6-3" type of excretory, Haplometra cylindracca and 

 Opisthioghjphe ranae are known to be of the stylet type. Prom these 

 considerations I conclude that Margeana calif orniensis develops from 

 a stylet cercaria. 



A comparison of figure 4 and figure 1 gives a number of interesting 

 points in regard to post-cercarial development in this species. In 

 the most immature individual found (fig. 4) no eggs were as yet 

 developed and the outlines of the vitellaria could not be discerned. 

 The testes (t.) and ovary (ov.) are relatively much smaller and fur- 

 ther back than in mature specimens. The excretory bladder (b.) is 

 also much shorter than in mature individuals. In the change from 

 the stage shown in figure 4 to that of figure 1 there is relatively a 

 much greater growth of the post-acetabular region, undoubtedly corre- 

 lated with the development of the coils of the uterus to hold the 

 enormous numbers of eggs produced. The ratio of the pharynx to 

 the oral sucker and of the ventral sucker to the oral sucker in the 

 immature individual (fig. 4) is very different from the usual condition 

 of the adult. Also the intestinal caeca of the immature specimen 

 reach to the posterior end of the body, and the whole surface of the 

 bodj r is covered with spines. 



