1 922.] A.. Oka : Hintdinea from the Inle Lake. 525 



position and present nothing particular compared with those of 

 other well-known species. 



Of the nephridia I counted sixteen pairs, which are situated 

 in the same position as those of Hemiclepsis marginala (12). The 

 openings could not be detected in surface views, so that their posi- 

 tion had to be determined by a study of sections. They lie, as in 

 many other species of the genus, in the furrow separating the first 

 and second annuli of the respective somites. 



The nervous system is composed of 34 ganglia connected by 

 longitudinal nerve trunks The first six are fused together to form 

 the circum-oesophageal ring. The last seven are likewise coalesced 

 in a single mass at the base of the hinder sucker. The remaining 

 ganglia are separate, arranged regularly one in each somite, except 

 near the anterior and posterior extremities where they are more 

 crowded. 



Annulation. As stated before, the somite limits are recogniz- 

 able at a glance in this species, as the furrows separating the 

 successive somites are more conspicuous than the interannular 

 furrows. Examined under a low power of the microscope a little 

 out of focus, the former alone are visible, while the latter disappear 

 completely, in such a way that the worm has now the appearance 

 of being uniannulate throughout. I have never seen a leech, 

 except perhaps Myxobdella annandalei Oka (14) from Hongkong, 

 which presented a somewhat similar appearance. Moreover, the 

 interannular furrows are not all of the same depth, that separat- 

 ing the first and second annuli of each somite being always less 

 deep than that separating the second and third annuli, so that in 

 many somites the first two annuli appear as a single broad ring, 

 especially at the margins. In most cases the three annuli com- 

 posing a somite have different widths ; as shown in the accom- 

 panying figure (fig. 2a) the second ring is the widest, then comes 

 the third which is a little narrower, while the first ring is always 

 the narrowest. 



There is apparently a certain amount of variation in the con- 

 stitution of somites at either end of the body according to the 

 age of the individual. This will be clear from the following table 

 which shows the annulation of two individuals, 9 mm. and 5 mm. 

 in length respectively. 



Somites. 



Number of rings 



in 



each somite 







A. 





B. 



i, ii 



. . 



1 





1 



iii, iv 





. 2 





1 



v, vi 





. . 2 





2 



vii, viii 





•• 3 





2 



ix-xxii 





•• 3 





3 



xxiii 





•• 3 





2 



xxiv 





. . 2 





2 



XXV 





. . 2 





1 



xxvi, xx vii . 



• • 



1 





1 



