172 ALFRED GIBBS BOURNE. 



by a pair of lateral commissures. Lateral commissures were 

 also observed ia the somites which contained the ova in the 

 female (somites 4 and 5). 



In the central region, the dorsal and ventral vessels pass 

 towards the sides and appear to form a sinus around the intes- 

 tine, Claparede thought to have observed this condition in 

 Fabricia armandi, and De Quatrefages in Araphicorina. 



Vessels pass to the head, but it was not possible to make out 

 their exact origin ; these dilate into a sinus at the base of the 

 peristomial tentacles (Claparede, ' Rech. Anat. sur les Anne- 

 lides, &c., dans les Hebrides,^ 1861, describes similar sinuses 

 at the bases of the branchiae in Fabricia quadripunctata 

 and calls them '' branchial hearts"), but vessels pass from them 

 into the palps only, a single trunk to each, which alternately 

 fills and empties, as is the case in Fabricia and in Polydora 

 and Spio. 



Nephridia. — It was impossible to determine definitely the 

 Nephridia; in somites 10 to 12 (fig. 4, Neph.) paired bodies 

 are seen at the base of the parapodia, which I take to be 

 Nephridia. 



In the third somite there are two bodies, the structure of 

 which could not be ascertained, owing to the amount of pig- 

 ment in the wall, but they are doubtless modified Nephridia 

 and function as tubiparous glands ; they open at the bases of 

 the parapodia on each side in the same somite. 



Gonads. — The sexes are distinct. The spermatozoa are 

 seen floating in various stages of development in the body 

 cavity in the thoracic somites 7, 8, and 9, but not in the abdo- 

 minal somites (fig. 4). 



They are confined to the central region of the somite around 

 the alimentary canal by a membrane. The spermatospheres 

 are not spherical, but much elongated rope-like bodies. 



They cannot be passed from segment to segment, and the 

 manner in which the spermatozoa are shed is uncertain. 



In the females the ova are found in somites 4 and 5 (fig. 2), 

 and attain a very large size in the body cavity ; their shape is 

 continually being altered by the movement of the wall of the 



