152 A ren icolidae 



lent to the writer by Prof. Mesnil, is shown in Fig. 65. As in 

 Arenicola (pp. 39-41) crotchets occur in the notopodia for a short 

 period only ; they are no longer present in two specimens of B. vincenti, 

 4 and 5 mm. long respectively, with twenty-seven segments. 



GILLS. The gills of B. vincenti are of a much simpler type than 

 those of Arenicola. Each consists of one, two or three, rarely four, 

 finger-like filaments, not more than '15 mm. long, each containing 

 an extension of the coelom and a vascular loop. The position of the 

 first gill is subject to variation : for instance, in the specimens 

 examined by the writer, the first branchiate segment is the 18th, 

 19th, 19th, 20th, 21st and 21st respectively. 1 The succeeding 

 segments, except perhaps the last or last two, are all branchiate. 



Gills begin to arise about the time the worm has attained thirty 

 segments, and then develop rapidly, for in a specimen with thirty- 

 six segments, gills are present on the 19th to 34th inclusive. 



HABITAT. Langerhans found B. vincenti living in small sand- 

 covered tubes, among algae, on the rocks of the beach of Teneriffe. 

 Prof. Mesnil collected his specimens in rock pools near Cape la 

 Hague ; the worms were inhabiting transparent mucous tubes, 

 which were generally situated on the lower side of the encrusting 

 calcareous alga Lithotliamnion. 



COLOUR. Langerhans states that his specimens were brownish. 

 Prof. Mesnil' s first specimen was a clear grayish colour, but his later 

 ones pale rose. Specimens preserved by him in formalin, and given 

 to the writer, have a pale pink colour. The pigmentation is much 

 less in amount than in specimens of Arenicola ecaudata of about the 

 same size. 



INTERNAL ANATOMY. The coelom resembles, in its relations and 

 proportions, that of an ecaudate Arenicola. The coelomic fluid 

 contains numerous oval and spindle-shaped cells and the genital 

 products. Septa are present at the anterior end of the first, third 

 and fourth segments, and throughout the gill region. There are no 

 septal pouches (PL XI, Fig. 32). 



The alimentary canal is similar to that of Arenicola, except that 

 the two oesophageal glands have a common duct. 



1 Langerhans records examples in which the first gill was borne on the 23rd 

 and 24th segments respectively. 



