PHYLUM PLATYHELMINTHES 



239 



vit 



of the testes and unite in the middle line posteriorly. The median 



duct formed by the union of the two vasa deferentia traverses a 



protrusible muscular organ, the 



penis (p), to open into the genital 



cloaca. At the base of the penis, 



where the vasa deferentia meet, 



the median^ canal is slightly 



enlarged to -"" form a rounded 



dilatation, the vesicula semincdis. 



Into the median canal open the 



narrow ducts of a number of 



unicellular glands, the prostate 



glands (pr). 



The female part of the repro- 

 ductive apparatus consists of 

 ovaries (germaria), oviducts, vitel- 

 line glands, utems, and muscular 

 sac. The germaria (ov.) are two 

 in number small rounded bodies 

 situated near the anterior end, 

 each connected with an elongated 

 duct, the oviduct. The two ovi- 

 ducts (od.) unite posteriorly to 

 form a short median common ovi- 

 dutt opening into the genital 

 atrium. With this cavity are 

 connected also the uterus (ut), a 

 median rounded chamber, and a 

 thick-walled muscular body, the 

 muscular sac (in.). Numerous 

 branching tubes the xitclline 

 glands (xit.) open into the ovi- 

 ducts. 



Reproduction is entirely sexual. 

 The oosperm is enclosed within a 

 protecting case or shell, which 

 contains also a quantity of food- 

 yolk derived from the vitelline 

 glands. When the larva has 

 reached a certain stage it de- 

 velops a temporary larval mouth 

 and gullet (see Fig. 218), and 

 swallows the food-yolk, by the 

 aid of which it grows rapidly. 

 The larval mouth disappears, and a new one the permanent 

 mouth is developed in its place. When the embryo leaves the 

 shell, it has assumed the characteristic shape of the parent. 



fit 



FIG. 184. Planaria. Reproductive system. 

 m. muscular sac ; 01: germarium ; ph. 

 pharynx ; p. penis ; pr. prostate ; tes. 

 testes ; ut. uterus ; v. d. vas defereus ; 

 rit. vitelline glands. (After Jijima and 

 Hatschek.) 



