in spite of that there is much that is not clear in the morphology and system- 

 atics of this group. Unfortunately, after the excellent work of Goto (Goto, 

 1894, 1899) the majority of researchers did not attach any significance to 

 a number of the most important characteristics in the description of species, 

 and did not mention them in the texts, accompanying their descriptions by 

 excessively schematic drawings, in which it is impossible to see even such 

 peculiarities as for instance the presence of common or separate apertures 

 of the ducts of the sex system. Hence, it is very difficult to utilize many 

 literary data and, as we shall show later, their authenticity is doubtful. 



This concerns, first of all, the structure of the attaching appa- 

 ratus. The latter in the typical case has the appearance of a powerful 

 sucker divided inside by muscular septa into a number of peripheral depressions and 

 one central depression, and the locations of the middle and edge hooks in 

 relation to the septa are strictly normal for the corresponding group within 

 the limits of Capsalidae. As a rule the majority of authors either do not p. 375 

 show the edge hooks altogether (Goto, 1894; Meserve, 1938 and others) or 

 show their location on the disc completely arbitrarily (MacCallum, 1921; 

 Price, 1934, and others). Without these data it is very difficult to decide 

 correctly the position of a given species within tne system of any subfamily 

 and sometimes even of a genus. Even more sad is the fact that very often 

 one cannot judge even the presence or absence of septa from the data of 

 different authors. In considerable measure the reason for this is that the 

 weakly expressed septa become so transparent during the process of the 

 preparation of slides in Canada balsam that they remain unnoticed. 



If we examine the attaching disc of Capsalidae, first of all our 

 attention is drawn by the presence of three basic types of structure. The 

 first type in its most primitive state corresponds to the type of the attaching 

 disc of Calicotylinae, i.e., it consists of 7 peripheral and 1 central 

 depression and the middle hooks (if they exist) lie in the two posterior septa^ 

 and on the anterior part of the disc there is one unpaired septum. In contrast 

 to Calicotylinae and Dasybatotreminae the edge hooks are located differently 

 along the edge of the disc, as is apparent from Fig. 278, A. This disc is 

 peculiar for Capsalinae and Megalocotylinae. The second type differs from 

 the first by the absence of the anterior unpaired septum, which never occurs 

 in Monocotylinae and which apparently is a secondary phenomenon in relation 

 to the structure of the disc of the first type. The nature of the location of 

 the chitinous hooks in this type is illustrated in Fig. 278, B. It is en- 

 countered in Trochopodinae in the new scope of understanding of this sub- 

 family. Finally the third type, peculiar to Entobdellinae and Nitzschiinae 

 and in the somewhat aberrant species of the subfamily Encotyllabinae, is 

 characterized by the complete absence of septa (see drawing in Fig. 278, C). 

 Further changes of the disc in the different subfamilies will be examined in 

 the corresponding places. Here we shall only note that if the origin of the 

 discs of the second type from the first does not arouse doubt then the question 

 about the primary and secondary absence of the septa in the third type is 

 very complex and apparently comes about differently in different groups. 



447 



