526 Records of the Indian Museum- [Voi,. XXIV, 



Thus, the larger individual (A) has 67 rings, while the smaller one 

 (B) has only 61. As the somites at the extremities are more 

 abbreviated in younger individuals than in older ones, it is evident 

 that the elaboration of the somites has progressed centrifugally 

 from the middle region toward both extremities. This is exaetty 

 the opposite of what we should expect, if the triannulate somite 

 represented the primitive condition, from which both biannulate 

 and uniannulate somites were derived by subsequent abbreviation. 

 An examination of the individual somites seems to confirm this 

 view. 



Somite i has only one ring. It bears a faint transverse groove 

 which, however, does not reach to the lateral margins. Somite ii 

 is clearly uniannulate, the pigment cup of the eye occupies almost 

 the entire breadth of this ring. Somites iii and iv are biannulate 

 in large individuals, but uniannulate in smaller ones. In the former- 

 case somite iii is composed of two rings of practically equal breadth, 

 somite iv, on the contrary, of an anterior broader and a posterior 

 narrower, the ratio of the breadths being about 2 to 1. Somites v 

 and vi are always biannulate, being composed of a broad and a 

 narrow ring. Somites vii and viii are triannulate or biannulate 

 according to the size of the individuals, the furrow separating the 

 first and second rings being confined to the median area in smaller 

 individuals. Somites ix to xxii are triannulate. Somite xxiii is 

 triannulate in large individuals but biannulate in small ones ; in 

 some cases it is difficult to decide whether the somite should 

 be considered as triannulate or as biannulate. Somite xxiv is 

 biannulate; somite xxv either bi- or uniannulate; somites xxvi 

 and xxvii uniannulate. The biannulate somites at the posterior 

 end of the body are invariably composed of an anterior broader 

 and a posterior much narrower ring. At the margins all the 

 triannulate somites appear as biannulate, as the rings 1 and 2 

 form a single broad tooth separated by a notch from the narrow 

 tooth formed by the ring 3. 



The chief peculiarity in the external morphology of this 

 leech is, as already stated, that the somite boundaries are recog- 

 nizable at a glance and the three annuli forming a somite are not 

 of the same size. By tracing the somites from the extremities 

 toward the median region, we can observe the various stages 

 through which the primitive uniannulate somite of the ancestral 

 leech gradually became the typical triannulate somite of the Glossi- 

 phonidae. First the somite became broader, then a narrow ring 

 was separated off from the posterior margin. The biannulate 

 somite thus formed next became triannulate by the separation of 

 a still narrower ring from the anterior margin. Afterwards the 

 three rings became equivalent in size, making it extremely difficult 

 to find out where the somite boundaries really are. 



This species presents a certain resemblance to the diagram- 

 matic figure of Placobdella emydae Harding (9), with which it. 

 agrees in the number of crop diverticula, the testes, and the posi- 

 tion of the genital openings. Both forms were also found attached 



