ization for which the presence of considerable differences between the sizes 

 of the 4th and the first 3 pairs of clamps is characteristic. At the same p. 420 



time, the absence of vaginal ducts in this species is apparently a secondary 

 phenomenon, just as in Octostoma. 



The genus Mazocraeoides deserves attention. At first glance 

 it seems the most primitive of the entire family. The presence of one testis, 

 which is a primitive sign is characteristic for this genus. However, the 

 structure of the attaching apparatus clearly bears the traits of secondary 

 changes. Thus, the attaching clamps of these worms are located, not on the 

 attaching disc but lie along the edges of the body, extending even into the 

 first half of the body. Taking into consideration the fact that the clamps 

 of Mazocraeidae are incepted at the places of the 2nd - 5th pairs of edge 



hooks it is possible to think that in the 

 •— ' present genus we first encounter the 



displacement of edge hooks from the disc 

 to the body of the animal in the post- 

 embryonic period, or with the develop- 

 ment of sex glands and other internal 

 organs inside of a strongly growing 

 attaching disc with simultaneous weak 

 development of the body proper of the 

 Fig. 298. Mazocraes alosae larva. One must suppose that the first 



Hermann, cOpulatory organ variation is less likely; however, they 



of an adult worm from the both indicate secondary changes in the 



gills of Alosa caspia (Eichw. ), structure in comparison with Mazocraes 



from the Delta of the Volga. and other "normal" genera. Undoubtedly 



secondary is also the structure of the copulatory 

 organ in which there are special chitinous plates in place of the small hooks 

 lying in the perpendicular plane in relation to the plane of the location of 

 both large hooks. One must think that the presence of a single 

 aperture for the vaginal ducts opening along the medial line of the dorsal 

 side is also a secondary phenomenon. Thus, in spite of the seeming 

 primitiveness, the Mazocraeoides are undoubtedly of a later origin than 

 the remaining genera of the families. 



In conclusion, one cannot fail to note that within the limits of the 

 family we see the evolution of the strengthening of the attaching contrivances 

 of the worms in two directions. One direction where this strengthening takes 

 place by means of strong development of the fourth pair of clamps is charac- 

 teristic for Pseudoanthocotyle. Another method we see in Mazocraeoides 

 where strong attachment is attained by means of the dispersement of the 

 attaching organs along a larger portion of the length of the body. The last 

 direction, as will be seen from what follows, is apparently more progressive 

 and is encountered in a number of highly organized forms. 



503 



