502 



ANNELIDA. 



drilus, Megascolides, etc., in which the salivary glands are supposed 

 to be modified nephridia, and in Octochaetus multiporus there are 

 nephridia in the posterior segments, which open both to the exterior 

 and into the rectal part of the gut, as well as internally into the 

 coelom (recalling the respiratory trees of Gephyrea), see p. 530. 



In the Eudrilidae, which have paired meganephridia, the ducts 

 of the nephridia branch in the body-wall, and form a network which 

 has several openings to the exterior. 



The nephridia are developed from certain structures in the embryo called 

 pronephridia. These are small cellular aggregations attached to the septa, one 

 pair in each segment, except in front. The first pair constitutes the head-kidney : 

 they open on the head, sometimes on the dorsal surface by the head pore 

 (Lumbricus), and occupy two or three segments. They may persist or disappear. 

 In the hinder segments they are at first straight rows of cells ending anteriorly 

 on the septum in a flame-cell with a vacuole containing a flame-shaped flagellum 

 (Rhynchelmis). This large terminal cell eventually divides up, loses its flagellum, 

 and forms the ciliated coelomic opening. 



As stated above, the plectonephric condition is preceded by a stage with one 

 pair of pronephridia in the segment. 



In Megascolides anstralis the pronephridia in the anterior part of the body 

 give off loops, which become disconnected, so as to form several separate nephridia, 

 of which one retains the coelomic opening, and forms the large nephridium of 

 the segment. 



Generative organs. 



FIG. 412. Generative organs of Lumbricus (after Bering). 

 T testes in X and XI; St the two sperm-rosettes (funnels of 

 vas deferens); Vd vas deferens; Ov ovary; Od oviduct; 

 Re receptacula seminis. One half of the sperm-reservoir and 

 the sperm sacs of one side have been removed. 



The Oligochaeta are all hermaphrodite. The 

 position of the 

 gonads varies in the 

 Limicolae ; but it 

 is fairly constant in 

 the Terricolae, there 

 being in this group 

 usually (Fig. 412) 

 two pairs of testes 

 placed in segments 

 10 and 11 respec- 

 tively, and one pair 

 of ovaries in seg- 

 ment 13 (except 

 in the Moniligas- 

 tridae). 



When there is only 

 one pair of testes, it 

 is in 10 in Typhaeus, 

 in 11 in Diachaeta 

 and Eudriloides, and 



