a very accurate understanding of correlations between the separate 

 groups of nnonogenetic trematodes. At the same time, we must keep 

 in nnind that the attaching fornnations of nnonogenetic trennatodes repre- 

 sents a complex system with a different degree of integration conse- 

 quently it is completely unjustifiable to equate the system to one charac- 

 teristic alone. It will be more correct to evaluate them as a complex 

 of characteristics linked correlatively with each other. 



In the chapter about individual development we have already 

 spoken (see page 99 ) about the tendencies and directions of the change 

 in the attaching apparatus, however, it is indispensable to return to this 

 question. 



As a study of the development of contemporary monogenetic 

 trematodes shows, there are two basic types of larvae of which generally 

 each is typical for one of the indicated basic ways of evolution of the 

 group, although the beginning stages of these ways are characterized 

 by adaptations to parasitizing the gills directly and begin to differentiate 

 themselves only later. This undoubtedly points to the great antiquity of 

 this way of development with a sufficient antiquity of separation, of both 

 ways because the larvae themselves are adapted to the free form of life, 

 but reflect by their morphological differences hereditarily consolidated 

 tendencies to the subsequent direction of the morphophysiological evolution. 



At the same time we see that in both group3 of larvae and 

 correspondingly in adult forms the changes in homologous and non- 

 homologous organs and formations take place in parallel fashion and 

 independently of each other. The reasons and circumstances connected 

 with this will be discussed by us later (page 464 ). 



Let us pause on the attaching armature of the worms of the 

 line of development of the monogenetic trematodes characterized by 

 the larva of the first type. 



As we saw in the re-creation of the promonogenetic trema- 

 todes, the latter apparently possessed numerous undifferentiated attaching 

 thorns which were possibly curved into a hook shape from the very be- 

 ginning of the formation of the group. Further process went along the 

 line of their qualitative change --morphological complication and 

 "improvement" [from the point of view of their adaptation to the basic 

 (chief, nobis) new function --attachment] and a quantitative --initially 

 only of decrease and then increase in the number of new chitinous 

 formations on the new bases (foundations, nobis) at the expense of (in 

 the shape of, nobis) new chitinous formations which were analogous to 

 the first. As we shall see, the latter is not quite clear. 



384 



