TUBIFEX RIVULORUM. 21 



nervous cords are difficult to make out, and I have only succeeded 

 in catching occasional glimpses of them. 



The reproductive organs present a complicated structure, and 

 many points of very great interest j but space is wanting here for 

 their elucidation, and they must be reserved for, perhaps, another 

 opportunity. I trust that the foregoing remarks may enable some 

 of our members to take an interest in this despised Httle worm, 

 within whose tiny compass so many lessons of physiological 

 importance lie hid. 



EXPLANATION OF PLATE L 



Fig. 1. — Webbed seta of Tubifex umbellifer, extremity only. 



,, 2. — Hooked seta3 of Tubifex rivulorum. 



,, 3. — Bristle-sacs with muscles. 



,, 4. — Ideal transverse section of worm, after Claparede, showing — 

 a, the integument ; 6, the layer of circular muscular fibres ; 

 cc, the six bands of longitudinal muscles ; ff, the furrows 

 between these bands into which the perivisceral cavity ex- 

 tends ; j^, the perivisceral cavity with its corpuscules ; c?, 

 the dorsal vessel ; v, the ventral vessel ; g, the glandular 

 hepatic cells of the intestine ; e, its inner vibratile epi- 

 thelium. 



,, 5. — Corpuscules of perivisceral fluid. 



,, 6. — Portion of segmental organ, after d'Udekem, showing 

 pouches. 



,, 7. — Tubifex rivulorum, slightly magnified. 



,, 8. — Glandular hepatic cells of intestine. 



,, 9. — Anterior segment of Tubifex rivulorum, after Mcintosh, 

 showing arrangement of blood-vessels : d, the dorsal ; v, 

 the ventral vessel ; pj>, the perivisceral ; ii. , the intestinal 

 branches. 



,, 10. — Three segments of Tubifex rivulorum further enlarged, 

 showing the intestine constricted by the segmental septa : 

 d, the dorsal, and v, the ventral vessels. In the first segment 

 the integument and ventral hooked setaj, st, are shown ; in 

 the second, the segmental organs, s, with their orifices, o ; 

 and in the third, the perivisceral corpuscules, cp. 



,, 11. — Portion of segmental organ from eighth segment of Limno- 

 drilus Hofi"meisteri covered with pyriform glandular cells. 



