154 



Arenicolidae 



maldanc are relatively very large. A mature specimen of Arcnicola 

 may contain several or many thousands of full-grown oocytes, but a 

 mature specimen of B. vincenti contains comparatively few about 

 120 were found in one specimen. The eggs of B. vincenti escape 

 by rupture of the body-wall in one or more of the posterior segments. 



SR 



Ov. 



NOT; 



NEUR. 



V.V. 



N.C. 



Fig. 67. B. vincenti. Transverse section through the fortieth segment. 

 D.V. Dorsal blood-vessel ; EP. Epidermis ; INT. Intestine ; M.CiRC. Circular 

 muscles ; M.LONO. Longitudinal muscles ; M.OB. Oblique muscle ; N.C. 

 Nerve-cord ; NEDR. Neuropodium ; NOT. Notopodium ; Ov Egg (oocyte) ; 

 SP. Mass of spermatocytes ; V.V. Ventral blood-vessel. X lift. 



N.GR. 



Fig. 68. B. vincenti. Young stages of development (after 

 Mesnil, 1898) ; N.GR. Nuchal groove. 



PERIOD OF MATURITY, DEVELOPMENT. Mature examples of 

 B. vincenti have been recorded only by Prof. Mesnil, who collected 

 them at St. Martin in August and September, 1898. The whitish 

 eggs were found around the tubes which the worms inhabited. 



To Prof. Mesnil we owe also the only observations on the develop- 



