TAPANESE LAND LEECHES. 



281 



followed by Blanchard (1892, etc.) bat we have then to disregard 

 wholly that portion of the l)ody lying in front of the fir.st pair of eyes. 

 Kennel (1886), in describing the land-leeches of South America, counts 

 the rinu's on tlie ventral side, beoinnini"- with the first Cünii)]ete rino- 

 behind the posterior margin of the mouth, but this method is still less 

 satisfactory than the hrst one, especially when Ave want t(3 mark })re- 

 cisely the position of the eyes or some other organs in the head region. 

 Lastly, Apathy (1888) counts every ring in the body, whether in 

 front of the first pair of eyes, or behind it. As this method seems to 

 be the least artificial, I have followed it in the present paper, as well 

 as in my former articles on leeches. It need not be added, that in so 

 doing I do not necessarily attrilxite to each apparent ring at the 

 anterior extremity of the body, the value of one morphological ring. 



In studying the external morphology of ten-eyed leeches, AVhit- 

 man (1885) |)oint3 out the occurrence of certain segmental sense- 

 organs on the first ring of every somite. If this were the case 

 throughout tlie wliole Order, the determination of the boundary of 

 somites would not have l)een a very difficult task. But, there are a 

 great many genera and species, in which, as in (Jrohdella, all the rings 

 constituting n somite look exactly alike, so that the method pro[)osed 

 and carried out by Whitman can not always be applied with success. 

 In such forms, Blanchard (1892 &c.) used the nephridial pores alone 

 as the starting point for the de*:ermination of the somites. In the 

 following diagnoses, I fixed the number of rings in a. complete somite 

 in each species, by means of the position of the nephridial pores and 

 the nervous ganglia, and for the determination of the numerical 

 order of the somites I counted them forward and backward from the 

 genital openings, whose position had been previously ascertained by 

 dissection. 



