EXCRETORY AND REPRODUCTIVE ORGANS 



4O1 



cells, one lying inside the other, and that there is sometimes also 

 a telescoping of cell within cell where the duct is single. In 

 Hirudo the same writer has described the nephridial funnel, 

 which has lost the simple character of that of Glossiphonia. 

 The funnel is represented by a cabbage-head-like mass (Fig. 

 207, /) of ciliated cells with no single definite outlet to the 

 exterior as in Glossiphonia. It appears to be an organ which 

 has lost its proper function a degeneration of the funnel being, 

 as a matter of fact, not unknown in the Oligochaeta, where it 

 may be carried to absolute extinction (Chaetogaster). In Bran- 

 chellion and Pontobdella the simple metameric arrangement of 

 the nephridia is to some extent lost, owing to 

 the formation of a network continuous from 

 segment to segment. It will be borne in 

 mind that the Oligochaeta are the only other 

 Chaetopods in which such a nephridial net- 

 work has been stated to exist. 



Male Reproductive Organs. In Hirudo 

 medicinalis there are nine, occasionally ten, 

 pairs of testes, which are round white bodies 

 arranged segmentally, i.e. a pair to each seg- 

 ment. From each arises a slender, somewhat 

 sinuous tube, which enters the common collect- 

 ing tube of its own side ; each of these is much 

 contorted at the upper end, the coiled portion 

 being termed the epididymis. From this they 

 enter a muscular penis which can be pro- 

 truded. This is the arrangement met with in 

 all leeches, save for the fact that the penis is 

 absent in some ; in Glossiphonia (see Fig. 

 208) this is the case. The number of pairs 

 of testes also varies ; and in Nephelis they are 

 no longer arranged metamerically. 



The testes arise as local proliferations of 

 the epithelium of the lateral coelomic cavities, 

 but from the somatic wall, not from the 

 splanchnic, as in the case of the ovaries to be 

 described later. A portion of the tissue 

 which is to form the testis grows out later- 

 ally into a thin cord, which is to become the vas effereus of that 



VOL. II 2 D 



FIG. 208. Nervous 

 system and repro- 

 ductive organs of 

 Glossiphonia plana. 

 x 2. (After Whit- 

 man.) gl, Prostate 

 glands ; n, iierve- 

 cord ; 0, ovary ; t, 

 testes. 



