600 M. Kowalewski: 



Nephridia commence usually in segment IX and occupy 

 the total length of a segment. Fuunel oblong oval. IY2 — 2 times 

 as long as broad, at its tip eut obliquely. Very long folded duet 

 enveloped in a compact mass of clear glass-like cells. 



Nervous system. Brain (Fig. 9, 27) heart-shaped, deeply 

 concave behind. 



Respiratory (branchial) organ looks like a long, very con- 

 tractile tube (Fig. 35, 55), formed by an immédiate prolongation 

 of the posterior end of the body backwards from the growing zone. 

 Its wall (Fig. 34, 55, 56) consists of: 1) dermal epithelium (with- 

 out glands), 2) circular and longitudinal subdermal muscle fibres, 

 3) prolongations of the dorsal and ventral vessels (in their normal 

 position), 4) intestinal ciliated epithelium, and 5) thick inner mass 

 of stellate cells similar to those in the genus Dero. It is capable 

 of two kinds of contractions: in the direction of the longitudinal 

 axis (Fig. 35, 36) and in radial direction, like the peristaltic con- 

 tractions of the intestine (Fig. 39. 40). It is eudowed with a consi- 

 dérable faculty of régénération (Fig. 35, compare Fig. 55). 



Reproductive organs. A. limnobius and A. pigueti become 

 mature at the beginning of summer, A. pluriseta at its eiid. 



Maie organs. Two pair of testes. First pair (Fig. 10, 19, 

 46, t.) in segment V, small, less developed, nevertheless producing 

 the sperm, but without any trace of any efferent way. The author 

 considers them a rudimentary organ, got by inheritance from ances- 

 tors in which it was hère formerly in fuU activity, as we see it 

 now in the Naididae. Second (normal) pair of testes (Fig. 46, t.) 

 in segment VI large, well developed. Sperm-funnelsin A. linmo- 

 bius (Fig. 1, 2) and A. pigueti (Fig. 16, 17) rather longer than broad, 

 with round opening, in A. pluriseta. (Fig. 44, 45) broader than long 

 with oval opening. Sperm-ducts as long as the distance from 

 funnel to atrium. Atrium in A. pigueti (Fig. 16, 17, 30 at.) small, 

 oblong oval, lying in front of the middle of segment VII, in A. plu- 

 riseta (Fig. 44, 45, 50, at.) more globular, at the inner side of the 

 penis-masses, in A. Hm?iobius (Fig. 1, 2, 11, at.) as very long sacs 

 occupying the whole place between thèse masses, a little backwards 

 of them. Prostata (Fig. 3, pr., aud ail cited above) massive, more 

 {A. pluriseta) or less lobate on the surface. A protracted pénis 

 was only observed in A. pigueti (Fig. 17, 23. p.). Its oblong oval 

 distal part covered with rings of délicate little cuticular lists. Ge- 



