102 Mr. E. Ray Lankester on distinct Larval and 



X. — On the Existence of distinct Larval and Sexual Forms 

 in the Gemmiparous Oligochcetous Worms. By E. Ray 

 Lankester, B.A. Oxon. 



In the ' Quarterly Journal of Microscopical Science ' for July 

 I have described the sexual form of Choitogaster Limnoii, 

 which differs from the gemmiparous larvae abounding through- 

 out the year on the Limnceus and Planorhis in the fact that 

 the number of set£e in each fasciculus is doubled, that there 

 are sixteen pairs of abdominal fasciculi instead of three or 

 four to each individual, that gemmiparity is discontinued, and 

 that a new pair of fasciculi developes between the cephalic and 

 first abdominal pair of fasciculi, four setse of which on either 

 side are not uncinated and bifid at the apex, but stunted club- 

 shaped organs. These I call " genital setee." In studying 

 the generative organs of No/is serpentina^ wliich swarms in a 

 very filthy pond on Hampstead Heath, which has furnished me 

 with LumhriculuSj Limnodrilus (new species), Enchytrceus 

 (new species), and two other species of No/is ^ I have ob- 

 served a somewhat similar change and development of " genital 

 setge," which do not appear to have been known to Carter 

 (who described the " spermatology " of a species of Na'is in 

 this Journal in 1858), nor to the late Jules d'Udekem (in his 

 description of Stylaria) ; nor have they been mentioned by 

 M. Edouard Clapar^de, to wliom, however, I dare say tliey are 

 known, since he has studied a species oiNais^ but, I believe, has 

 not published the description of it among his other invaluable 

 contributions to this branch of zoology. I therefore conclude 

 that these modified setee and their position are unrecorded 

 hitherto. 



In Na'is serpentina and other species of Nais, five pairs of 

 ventrally placed fasciculi succeed to the mouth, indicating a 

 pharyngeal region. There are no dorsal seta; in this region. 

 Immediately after the fifth pair the intestine commences ; that 

 is to say, the alimentary canal is contracted and its walls are 

 covered by a layer of coarse cells — the so-called hepatic tunic. 

 Corresponding to the sixth pair of ventral fasciculi is a pair of 

 dorsal setaj, thick, short, and awl-shaped in N. serjK'.ntina ; 

 these continue thenceforward, along the body, with the ven- 

 tral setee. The bristles of the ventral setee are curved, with a 

 hooked bifid apex ; two, with a growing third, is the usual 

 number in a fasciculus. When the generative organs com- 

 mence their development, the distance between the fourth and 

 fifth ventral fasciculi enlarges very considerably, and a new 

 pair of fasciculi makes its appearance, placed a little nearer the 

 middle line, and therefore closer together, than the other fasci- 



