100 ]\ir. E. Raj Lankester on OlicjoclicBtoaa Annelids. 



in wliicli there are ova and spermatospheres exhibit no trace of 

 the genital seta^ ; and, again, Avhen these appear, no trace of 

 spermatic reservoirs, which do appear hater, is to be seen. I 

 have to add to ray former description, that the genital setae are 

 not " stumpy," as there stated, except when young ; they ulti- 

 mately assume the same proportions as those of Nais (Ann. & 

 Mag. Nat. Hist. 1869, vol. iv.), but exhibit a very slight notch- 

 ing of the apex, a trace of bifurcation. The fascicles of common 

 setaj near which they lie indicate a distinct segment, so that there 

 are two superadded to the larval series between the cephalic and 

 abdominal series. Some distance anteriorly to these seta3 a pair 

 of spermatic reservoirs or pouches are developed, which, as I 

 surmised at the time of my description of the worm, had not 

 had time to make their appearance in the specimens formerly 

 examined. These spermatic pouches were ciliated internally. 

 At the base of each tascicle of genital setas a very delicate and 

 short vas deferens opens, not longer than a seta itself, ciliated 

 within, but without any expanded trumpet-like extremity. 

 This I had not seen in specimens previously to this autumn, but, 

 from analogy with Nais, supposed such a simple vas deferens 

 to exist. The very gradual and bit-by-bit development of the 

 genitalia in the Naididaj is remarkable, and likely to lead to 

 misinterpretation ; but when we lind spermatic pouches con- 

 taining spermatozoa, we may feel sure that copulation has 

 taken place, and hence that development is complete. Con- 

 sequently there is not the same doubt about Nais as about 

 Chwtogaster. In Nais serjjentina a very large pair of sper- 

 matic pouches open at the fourth pair of fascicles ; between 

 these and the normal fifth pair arc the genital setaj, with very 

 short, simple ducts opening at their sides (the vasadeferentia). 

 There is clearly no " entonnoir vibratile " to these ducts 5 

 they are not longer than one of the seta3, and are very hnely 

 ciliated ; they are so delicate and transparent as to be imper- 

 ceptible generally through the dense cellular layer of the cli- 

 tellus. TJie ova in the Naididge float freely in masses in the 

 perivisceral cavity, Avith one ovum enormously larger than the 

 rest. I have observed one ovum in N. ser2)entina occupying 

 three whole segments of the perivisceral cavity. 



The cuticle of the sexual Chatogaster limncei is very finely 

 striated vertically, as seen in optical section. It was not sufli- 

 ciently figured in my paper on this form. 



8. Sources of discrepancy. — It cannot be too strongly insisted 

 on that observations made at different seasons on the same species 

 of Oligochajta may lead to different results. The differences of 

 some writers are thus explained. It is necessary to follow 

 each of these worms at all seasons of the year.^ from its deposi- 

 tion as an ovum to its natural death after a full life-period. 



