290 ASAJIRO OKA; ON SOME NEW 



the mouth ;ire always distiact, but the farrow that separates them on 

 the ventral surface is mucli less conspicuous than the one following it. 



The portion of the body directly following upon the head proper 

 may be called the neck. In this region, there seems to occur some ab- 

 breviation of the somites, though not to the same extent as in the 

 head. Owing, however, to the completely uniform appearance of the 

 rings, I am not able to give the manner in which this abbreviation 

 takes place. 



CliteUum. The number of the rings embraced by the clitellum is, 

 in the three species of OrohdeUa, 12, 19, and 24 respectively. This 

 difference is caused, not by tlie difference of their relative positions, 

 but solely by the difference in tlie number of rings in a complete 

 somite. In all the species, the clitellum occupies a space correspond- 

 ing- to three somites in leng^th. In Orohdella Whitmaid and Orobàella 

 oc^o«rtr/rt the number of rings in the clitellum is exactly three times 

 that in a somite. In Orohdella Ijinidi there is one ring more. The 

 position of the clitellum in relation to the somites can clearly l)e under- 

 stood from PI. XXIX, where the corresponding somites of the three 

 species are placed side by side. The somites X and XI, tli;it bear tlie 

 genital orifices are completely incUided in the clitellum, while the 

 somites IX and XII are only partly taken in in the formation of the 

 fore and hind portions of that organ. The somite IX has 8, 5, or 6 

 rings modified, according to the species, [n the somite XII only one 

 or two rings are modified, all the remaining rings lying outside the 

 clitellum. 



That in ( h-ohdelhi Ijiiiud the clitellum embraces one ring too many 

 to correspond exactly t<3 three somites in length, seems to be worth 

 notice. As may be understood from the figures in PI. XXIX, the 

 furrows that form the boundary of clitellum in Or. IVhitnuini and Or. 

 octonaria fall upon the rings ol and 49 in ( h-. Ijimni. Xow, as a ring 



