102 
MK. E. C. BOUSEIELD ON THE 
only be so called for convenience ; since for the greater part of 
its length it runs along the side or lower part of the intestine 
embedded in its wall, only becoming free when it reaches the 
junction of the latter with the stomach. From this point it is 
, connected by a varying number of contractile loops with the 
ventral vessel, and terminates exactly as in Nais. Iu the bran- 
chial area the circulation between the dorsal and ventral vessels 
is carried on as follows : — The abdominal vessel, running back- 
ward undivided to the boundary of the mucous layer of the area, 
divides into two branches which run right and left round its 
margin. Each of these main branches gives off at least three 
secondary oues, one to each of the branchia of its own side, which 
runs to its summit and down again without breaking up into a 
capillary network ; whilst the third, also undivided, runs obliquely 
across the area, the continuation of the main branch running on 
round the margin. All these branches again unite to form a 
common trunk, which joins with a similar one from the opposite 
side to form the commencement of the dorsal vessel. 
The specialization of the termination of the hinder portion of 
the intestine does not appear to have any effect in abrogating the 
general respiratory function of that tube ; doubtless an advantage 
to these worms, which spend so large a portion of their lives in 
crawling im the mud in search of food. It should be remarked 
that the tube is much too narrow to admit of the branchial area 
being drawn into it when expanded ; nor is the tube wide enough 
to give room for the bristles, the latter being always much curved 
when within it ; and though the worm is able, as a rule, to turn 
round with facility, yet it sometimes happens that it becomes 
fixed in the tube in so doing, and is quite unable to extricate 
itself. 
Distribution of Species. 
With the exception of Dero Mulleri, received from Mr. Bolton, 
of Birmingham, I have found all the known forms within a short 
distance of London. The richest huuting-grounds are without 
doubt the tanks at Kew and at the Royal Botanic Society’s 
Gardens, Regent’s Park. The latter locality has furnished a 
species, the only one whose indigenous character is doubtful, viz. 
the beautiful D. furcata, the finding of which and the difficulty 
of obtaining any reliable information about it, first led the writer 
to undertake the study of this genus. Here also he first found 
