assertion (Andre, 1910b) of the absence of these lenses among Polystoma 

 integerrimum Froelich is erroneous and is based on a study of small 

 numbers of young individuals; the presence of lenses in a number of mono- 

 genetic trematodes was verified by us not only on live subjects but also on 

 slides stained with the usual histological colors. Among forms having a 

 single eye, the eye is usually equipped with two lenses which enables us, 

 during the study of live subjects, to suggest that such an eye is a result of 

 the fusion or nnerging of the two eyes first existing in phylogenesis. Eye- 

 nerves are usually very short and emerge from the dorsal side of the 

 anterior part of the head ganglia. As Goto accurately points out, among 

 adult monogenetic trematodes the eyes are in the process of disappearing 

 and apparently do not function. 



Fig. 77. Polystoma integerrimum Forelich, two eyes from one side of the 

 body, semi-diagrammatic. Enlarged about 1300 times (According to Andre, 

 1910). 



From all of our observations, it is clear that the growth of the 

 eyes occurs only during the tinne of the development of larvae in the egg; 

 once it emerges from the egg its eyes grow no more and in many forms the p. 54 

 eyes are subjected to reduction or even complete disappearance during onto- 

 genesis. 



Sex System. All monogenetic trematodes without exception are 

 hermaphrodites. They usually have one common sex pore ( porus genitalis 

 Qorrmvunis ) , leading into the sex atrium into which opens the seminal ejacu- 

 latory canal or the male copulative organ and finally the uterus; rarely there 

 are separate openings of the male and female sex systems; sometimes the 

 seminal ejaculatory duct opens into the terminal part of the uterus. Usually 

 the common sex opening is located nnore or less medially on the ventral 

 side of the body, posterior to the esophagus or posterior to the bifurcation 

 of the intestinal trunk; more rarely it is located slightly to the side in front 

 of or behind the intestinal trunks, or it can be displaced completely laterally. 

 In addition to the common sex pore, among a majority of forms there exist 



49 



