systematics of a number of groups of monogenetic trematodes .appearing as 

 a good representative diagnostic sign. For various groups of monogenetic 

 trematodes the presence of a particular type of copulatory organ is charac- 

 teristic. Thus the lower Monogenoidea- -Protogyrodactylidae , Dactylogyridae, 

 Tetraonchidae , Diplectanidae , Amphibdellatidae and others have a chitinous 

 copulatory organ, Monocotylidae--a muscular penis usually weakly developed 

 but often equipped with a chitinous pipe; Capsalidae and groups close to them 

 have an unarmed penis, usually very powerful. Among Gyrodactylidae, 

 Polystomatidae , and Sphyranuridae , a small sucker— type copulatory organ 

 with a corona of chitinous hooks is characteristic. Among the highest 

 Monogenoidea (Mazocraeidae , Microcotylidae and others) the penis for the 

 most part is weakly developed, but on the other hand the chitinous hooks 

 in the sex atrium are powerfully developed. The only genus which has no 

 copulatory organ at all is Diplozoon, among representatives of which the 

 terminal part of the seminal duct of one individual grows together with the 

 ducts of the female sex system of the other. 



The fenaale sex system is of variable structure, differing even 

 within the limits of a single systematic group. Basically it is represented 

 among monogenetic trematodes by two large glands --ovary and vitelline, 

 supplementary glands, and a nunnber of ducts serving for the egression or 

 excretion of the glands, for the preservation and for the reception of sperm 

 and the preservation and egression of the eggs. As a rule all monogenetic 

 trematodes are oviparous with the exception of one viviparous fannily - 

 Gyrodactylidae. The anatomy of the female sex system of the latter is 

 much altered in connection with the live -bearing habit and will be succintly 

 characterized separately at the end of the description of the female sex 

 system. 



The ovary among monogenetic trenaatodes occurs singly and has 

 varying shapes and sizes and in a majority of cases is located in the anterior 

 part of the body in front of the male sex glands. In rare cases the ovary is 

 displaced to the posterior half of the body and as an exception (for instance 

 Vallisia and others) it is located behind the testes. The form of the ovary 

 among fresh water Monogenoidea is for the nnost part rounded (Fig. 97A), 

 and more seldom elongated (Fig, 97B), with a flask-shaped posterior part; 

 whereas among the marine species the second form of ovary is the most 

 common. Often the ovaries are strongly lengthened and significantly curved 

 in the anterior part and in the posterior part they form not a flask shape, 

 but a palmate shape (Fig. 97B). In certain cases the ovary is divided by a 

 constriction into more or less equal parts. The flask type part of the elon- 

 gated or the corresponding part of the round ovaries corresponds to the 

 oogonial chamber and contains the early stages of the developing egg cells. 

 The envelope of the ovary is of cellular structure and consists of flat, spindle- 

 shaped cells; in the period which follows the laying of the eggs the cells of this 

 envelope can strongly increase in size and possess the ability of seizing and 

 digesting the unused egg cells (see page 84). 



p. 66 



61 



