class of parasitic flatworms and not as a family entering into the compo- 

 sition of the subclass Cestodaria of tapeworms. At the same time, the peculiarities 

 of the structure of Gyrocotylidae are such that on the one hand these worms 

 are undoubtedly very close to Monogenoidea and on the other--to Cestoidea 

 and thus occupy an intermediary position between these two classes. 



The researches on the development of monogenetic trennatodes 

 which were conducted by us at that time forced us to attribute a much 

 greater significance to the larval stage and to the chitinous armature of its 

 posterior end. On the basis of this we came to the conclusion about homology 

 of the initial larval stages of tapeworms, Gyrocotyloidea, and monogenetic 

 trematodes. In connection with this, and also on the basis of the somewhat 

 re-examined theory of the cercomere of Janicki (Janicki, 1921), we established 

 that the origin of tapeworms from Monogenoidea-like ancestors should be 

 considered as more probable and that the intermediary group between these 

 classes is Gyrocotyloidea. All these 3 classes represent a special branch 

 in the development of flatworms. The presence of a cercomere in the larval 

 stage is characteristic for this branch, in connection with which we have 

 united them into a special superclass Cercomermorphae descending from 

 Rhabdocoela independently of digenetic trematodes. 



Such is the basic content of our work of 1937. The views ex- 

 pressed are completely held by us also at the present time. During the 20 

 years which have elapsed since then, a whole nunnber of specialists have 

 joined our point of view. Thus, the system which was proposed by us was 

 accepted in a number of works of Soviet parasitologists. In addition to that, 

 it is used by A. P. Markevich (1950, 1951) in his re'sume''s. V. M. 

 Beklemishev (1952) accepted it partially, he separates Monogenoidea into 

 an independent class but retains Gyrocotyloidea in the composition of 

 Cestoidea — Cestodaria. V. A. Dogiel in his last work, "Oligomerization of 



Homologous Organs as One of the Main Directions of the Evolution of 

 Animals" (1954) also accepts the system proposed by us. It is accepted in 

 the work, "Large Practical Work in the Zoology of Invertebrates, " which is being 

 prepared for publication under the direction of V. I. Polianski, etc. 



During the current period objections to it have been expressed 

 only by D. M. Fedotov in his survey of studies on the phylogeny of the in- 

 vertebrates of U.S.S.R. during the last 20 years (Fedotov, 1938). D. M. 

 Fedotov briefly outlines our work and then writes: "The views of Bychowsky 

 on phylogenetic relationships in the system of parasitic flatworms are so 

 far insufficiently substantiated by facts. He attributes principal significance 

 to the differences in structure of monogenetic and digenetic trematodes and 

 to the similarity- -only significance as converging characteristics. 



In order to underline the important meaning of the presence of the attaching 

 disc with the hooks on the posterior end, Bychowsky bypasses the differences in the or- 

 ganization of the monogenetic trematodes and tapeworms, even though, be it in connection 

 with the sex system, the differences which he himself recognizes 



564 



