THE TREMATODA 



tion. It appears to serve for the conveyance of superfluous yolk 

 to the intestine, where it will serve as food. 



(3) In the Malacocotylea and Aspidocotylea there is no vagina, 

 a fact that is associated with the much greater size of the uterus, 



-TZZZZZ^- 



Fio. XXII. Diagrammatic Transverse Sections to show the Relations of Various Parts of 

 the Female Ducts in the Three Orders of Trematoda. 



1. A Malacocotylean, showing Laurer's canal (/). 



2. An Aspidocotylean. The "yolk receptacle" (/) arises from the oviduct in the same 

 position as does Laurer's canal. 



3. A Heterocotylean (the lowest figure). The canal (/) is here called "genito- 

 intestinal canal." The right and left vagina (kk) are represented as entering the median 

 vitelline duct (</). In some cases they join the transverse vitelline duct ; one or both may be 

 absent. In all the figures : a, germarium, showing the distal syncytium and proximal germ 

 cells ; bb, germ duct or duct between the germarium and ootype ; c, shell glands set round (d) 

 the ootype, whence the duct is continued as uterus (c) ; g, median vitello-duct ; h, right and 

 left transverse vitello-ducts ; i, intestine, which in Fig. 2 is represented dotted; "Laurer's 

 canal " passes upwards behind it (see Fig. VIII. j). 



These organs do not lie in one plane, the figures represent "projections" in a vertical plane. 



which contains a very much larger number of eggs than in the 

 Heterocotylea, and often comes to lie behind the testes. Nor is 

 there a connecting canal between the vitelline duct and the 

 intestine, but in place of it there is a narrow canal, first dis- 



