and among Diplasiocotyle johnstoni Sand, three pairs of edge hooks and 

 finally Microcotyle mugilis Vogt has, besides edge and middle hooks, still 

 one more pair of attaching clamps] , Diclybothriidae, five pairs of edge 

 hooks and two pairs of middle hooks. For representatives of these groups 

 it is characteristic that all hooks, the lateral as well as the middle, do 

 not grow at all during the postembryonic period. As a rule they are either 

 retained unchanged during the entire life or are replaced by a clamp or 

 are even discarded from the body of the animal (see page212 ). The excep- 

 tion is represented by Mazocraeidae among which, during the postembryonic 

 period, there appears still one more pair of middle hooks which (and only p. 101 



they) grow for a sufficiently long period and considerably, and Diclybothriidae 

 among which the relationships are somewhat more complicated (see further). 

 Within the limits of this group we see certain tendencies toward the decrease 

 in the number of edge hooks among specialized species(Discocotyle , Diplozoon, 

 Dipliasiocotyle) . Finally it is extremely curious that the attaching clamps 

 of the first four pairs are incepted on the bases of the edge hooks, which 

 apparently enter into the composition of the chitinous parts of the clamps 

 to some degree. Among monogenetic trematodes which have more than 



four pairs of clamps, all incepted after the first eight are formed without 

 the participation of edge hooks, and by this they differ principally from the 

 preceding ones. V. A. Dogiel (1954) writes on the subject: "From here 

 we can make the following essential conclusion: in the first place all the 

 anterior clamps of Microcotylidae have a different origin than the four 

 posterior(pairs , --B,B. ) and because of that are not homologous to them: 

 in the second place, because of what has just been mentioned, the formation 

 of numerous anterior clamps must be considered not as polymerization (that 

 is the multiplication of a number of homologous organs) but as a numerous 

 (plural, nobis) inception of new organs not homologous to the posterior -- 

 four (pairs, -- B.B. ) clamps. " Subsequently, the «_lamps of the larvae 

 which have relatively very small sizes grow considerably. Their growth 

 differs significantly from the growth of the hooks because all the parts of 

 the clamps are incepted at once, but in small sizes, and after that they grow 

 equally in all their parts. 



A few words about middle hooks in the larvae of this group. 

 Middle hooks of the larvae of Mazocraeidae, Discocotylidae , Diclidophoridae , 

 and the first pair of middle hooks of the larvae of Microcotylidae generally 

 strongly resemble the edge hooks in their shapes and differ nnainly in their 

 somewhat larger sizes. It seems to us that, taking into consideration their 

 appearance in the embryonic period at the same time with the edge hooks and 

 also the places of their inception, it is more correct to consider them as the 

 sixth (more precisely the first ) pair of edge hooks; whereas the second pair 

 of middle hooks, which is incepted in the embryonic period among Micro- 

 cotylidae and in the postembryonic period among Mazocraeidae, clearly 

 differs in structure and is not equivalent to edge hooks. 



103 



