224 ^^- A. and W. G. MacCallüm, 



that the original papers of Van Beneden & Hesse ') were reviewed 

 by Paeona & Perugia in their table and to this we have added 

 the description of M. acanfhurum from another paper by the latter 

 authors. Linton ^} has described another form M. incisa but it is 

 hardly possible from his description to place this species exactly. 



In all these papers rather more stress is laid by the authors upon 

 certain extern al characters than upon the arrangement of the inter- 

 nal Organs and perhaps this is desirable, for in the papers of Goto 

 at any rate it is difficult to raake out the slightest Variation in the 

 arrangement of the female genital organs in the twelve species de- 

 scribed and depicted by him. He emphasizes, however, the position 

 of the genital pore with relation to the bifiircation of the intestine, 

 the character of the lateral coeca of the intestine and the number 

 of lobules in the festes while the earlier authors fall in many in- 

 stances to record this latter point. On the other hand, Paeona & 

 Peeugia describe very miuutely the armature of spines about the 

 genital opening, and base their determination of the species largely 

 upon this distinctive character. None of these authors has described 

 any penis or ejaculatory apparatus in the forms of Microcotyle, 

 although, as will be seen from the descriptions and drawings, we 

 have found this organ present in three . of our four species, and 

 quite completely developed. Nor has any of the few authors who 

 have concerned themselves with the anatomy of Microcotijle paid 

 more than the most cursory attention to the character of the 

 supporting framework of the suckers upon the caudal disc. This, 

 however, is a perfectly constant feature of each species and appa- 

 rently has a definite specific importance in the distinguishing of the 

 species. We wish especially to emphasize the value of the study 

 of the skeleton of these suckers and hope that it may be possible 

 for someone to restudy those forms which have already been de- 

 scribed with this point in view. We should recognize then, as 

 features of value in determining species. the following things : 



1. The form of the body and the relation of the caudal disc, 

 especially as to whether it is symmetrically or asymmetiically 

 attached. 



2. The number of suckers which it bears and particularly the 

 arrangement of the skeletal framework of these suckers. 



1) Van Beneden et Hesse, in: Mem. Acad. Sc. Belg., 1864, 

 Vol. 134. 



2) Linton, in: Publ. Carnegie Inst. Washington, No. 133, 1910. 



