66 
Proceedings of the Royal Society of Edinburgh. [Sess. 
The brain of B. vincenti consists, in the specimen in which it is most 
highly developed, of a median anterior lobe, and a pair of large middle and 
of small posterior lobes. These last were not recognisable in other 
specimens examined. The middle dorsal region of the brain is situated 
near the external surface, the prostomial epithelium which overlies it being 
very thin. The dorsal part of the brain is cellular, the ventral part fibrous. 
The oesophageal connectives arise from the middle region of the brain, and, 
after traversing the peristomium obliquely backwards and ventrally, unite 
near the middle of the following achaetous segment. The ventral nerve- 
cord, which is apparently non-ganglionated, lies immediately below the 
epidermis (fig. 5). Giant nerve-fibres are not present. 
The eyes are situated in the sub-epidermal tissue of the prostomium. 
Each eye consists of a cup-shaped mass, about 6 to 10^ in diameter, of 
brownish pigment-spherules, in some cases with the addition of a lens, 
situated in the mouth of the cup. Statocysts are absent, and the nuchal 
groove is feebly developed (p. 62). 
The published references to the nephridia of B. vincenti give the 
impression that the number of these organs is subject to variation. Professor 
Mesnil * * * § stated that segmental organs, more or less darkly pigmented, were 
present in the fifth, sixth, seventh, and eighth chgetigerous segments. In 
the following year j* he referred to the presence of four or five pairs of 
nephridia. Professor Fauvel J attributed to this worm four pairs of 
nephridia, but later § stated the number as three to five pairs, with pores in 
the fifth to the ninth chsetigerous segments. Drs Gamble and Ashworth || 
found only two pairs, having openings on the fifth and sixth segments, and 
remarked that the internal ends appeared to be without funnels. The 
writer has examined the nephridia, as far as has been possible in the limited 
amount of material at his disposal. In each of the five specimens suitable 
for the study of these organs, only two nephridiopores could be seen, 
situated immediately ventral H and slightly posterior to the fifth and sixth 
neuropodia. The aperture of the second nephridium is usually slightly 
larger than that of the first. That only two pairs of nephridia are present has 
been ascertained definitely by dissection of one specimen and examination 
of serial sections of two others. A diagram of the nephridia is given in the 
* Bull. Sci. France Belg., T. xxx. (1897), p. 158. 
t Zool. Anz., Bd. xxx. (1898), p. 636. 
X Bull. Sci. France Belg. y T. xxxii. (1899), p. 291. 
§ Mem. Soc. Nation. Sci. Nat. Math. Cherbourg , T. xxxi. (1899), p. 166. 
|| Quart. Journ. Micr. Sci. y vol. xliii. (1900), p. 537. 
IF In Arenicola the nephridial apertures are invariably just behind the dorsal ends of the 
neuropodia. 
