CHAETOPODA. 603 



the organ, e. g. in the anterior somites of the tubicolous Ophelia, or it may 

 be entirely wanting as in the posterior somites of the same animal. So 

 far as is known it is not represented in the Errantia, nor in some Tubicola, 

 e. g. Hermella. The remaining part of the nephridium is usually short in 

 Polychaeta, but long in Oligochaeta, and disposed in loops (p. 204). The 

 whole organ is either contained in a single somite, as in most Polychaeta, 

 or the funnel opens into a somite anterior to that in which lie the ciliated 

 tube and external aperture as in Oligochaeta^ iheAlciopidae among Errantia 

 (Claparede), and the larval nephridia of Capitella (Eisig). The nephridia 

 sometimes enlarge at the reproductive season, as in Spio Mecznikowianus 

 and the female somites of the hermaphrodite Microphthahnus. Certain 

 important variations have been observed. The nephridial funnel is absent 

 in the Oligochaete family Chaetogastridae, The number of nephridia in a 

 somite is increased in the terrestrial Oligochaete Acanthodrilus multiporus 

 (p. 204) and in the Capitellidae. Natomastus in this family has occasionally 

 more than one pair in a somite ; Capitella capitata on the contrary has 

 always 3-4 pairs in the anterior somites in which they occur, 4-5 in the 

 median, 5-6 in the posterior. Moreover the nephridia themselves in this 

 instance have remarkable peculiarities. There may be 24 funnels to a 

 nephridium ; two adjacent nephridia may be connected by a tube ; and the 

 duct of each nephridium divides into two main branches, and each branch 

 into 4-5 minute tubules which probably open externally by separate pores. 

 The nephridia of the aquatic Oligochaeta situated in the genital segments 

 atrophy before the sexual ducts develope ; they persist in the terrestrial 

 Oligochaeta side by side with the genital ducts. 



The Oligochaeta are hermaphrodite, the Polychaeta of separate sexes 

 with a few exceptions, such as certain Hesionidae and Nereis massiliensis 

 among Errantia, and among Tubicola certain Serpulidae (Amphiglena, 

 Laonome, Salmacina, Protula, Spirorbis Pagenstecheri, Sp. connmmis}. 

 The sexual organs in Oligochaeta are contained in the anterior somites, 

 and there is either a single pair, or in terrestrial forms two pairs, of testes 

 and a single pair of ovaries placed in different somites, the ovaries behind 

 the testes, except in Plutellus. The organs are attached either to the 

 posterior face of a septum or to the nerve-cord (Naidomorphd). The 

 corresponding organs of Polychaeta are closely attached to a blood-vessel L . 



1 Cosmovici is followed in this account. He found the sexual organs developed in Tubicola on 

 a vessel in relation with the nephridial funnel and tube (? Arenicola) ; on branches of a median ventral 

 vessel ( Terebella giganted] ; or of an infero-lateral vessel (Spirorbis} ; on the intestinal walls 

 {Chaetoptcrus} ; or on the anterior aspect of a septum vis d vis to the nephridium (ffermella). As to 

 the Errantia, he found the glands attached, in Nereis, to the supra-nervian vessel ; in Marphysa 

 (Etmicidaej to the branchial vessels proceeding from the supra-nervian, on the section intervening 

 between that vessel and the nephridial funnels ; in Plermione and Sthenelais (Aphroditidae] to a 

 vessel on the posterior aspect of the septa ; in Cirrhatulus to a vessel on the anterior aspect of 

 the septa. The organs are present in a large number of segments in Errantia. 



