expressed not only in the common nature of origin of secondary attaching 

 disc or discs above the primary, but also in the nature of the location of \ 



chitinous structures and also, in separate cases, in the form of the latter 

 (see Figs. 181 and 313). It is interesting to note with this that the 

 similarity between Acanthocotylidae and Diplectanidae, however, is not only 

 in this structure, but also in the nature and location and the form of the 

 ovary. In both families the ovary is singularly retort-shaped and among 

 representatives of both fannilies its extended terminal part loops around 

 one of the trunks of the intestine, a peculiarity not widely distributed among 

 Monogenoidea. ^ Together with this, both families pertain to different sub- 



467 



1 



An ovary of similar shape and location exists also in a number of 

 Monocotylidae . 



orders of Dactylogyridae (sic), and the absence of direct links between these 

 does not arouse any doubts. 



Fig. 313. Acanthocotyle williamsi 

 Price, part of the chitinous plates 

 of the secondary attaching disc of 

 worm from the skin of Raja 

 rosispinus G. and Town, near the 

 eastern region of southern Sakhalin 

 (Sea of Okhotsk). 



One can think that the origin 

 of the septa on the attaching disc of 

 Monocotylidae and Capsalidae un- 

 doubtedly took place independently of 

 each other; this is even more probable 

 for Dionchidae. Thus, similar 

 structures of the transformation of 

 homologous organs are the result of the 

 height of organization (the degree of 

 advancement of organization, nobis) 

 and their converging nature. We 

 shall note along the way that one can 

 also attribute the appearance of septa 

 of the attaching disc in Tetraonchoididae, 

 which are rather far removed from 

 both the above mentioned families, 

 to the same category of facts. Con- 

 vergent similarities of similar order 

 arise not only in progressive develop- 

 ment, but also in the processes of 

 Thus, this is well apparent in the exannple of 



morphological regression 

 the change of the attaching apparatus in Hexabothriidae, Diclybothriidae 

 and Hexostomatidae. For the first, the disappearance of the chitinous arma- 

 ture during inception of the first pair of clamps chronologically, is charac- 

 teristic, as is their transformation into suckers which have only a muscular 

 nature. Inasmuch as the posterior part of the disc retains insignificant sizes^ 

 whereas the anterior one strongly grows, an impression is formed that the 

 disc bears 3 pairs of clamps or suckers. In Diclybothriidae, among which 



560 



