STEUCTUEE OP UEOCH^TA AND DICHOGASTEE. 
237 
mental blood-capillaries with the surrounding medium. These 
capillaries were perfectly obvious since they were gorged with 
blood ; asuming for the present that they open by means of 
pores, it would no doubt be the case, as the Sarasins suggest, 
that capillary atti’action would prevent the blood from leaving 
the body. But when the body of the worm is contracted by 
the preservative fluid the blood would surely be driven out 
through the pores. Nor can it safely be said that the con- 
traction of the epidermic cells would be sufficient to occlude 
the orifice of the blood-capillary; this would be forced open by 
hydrostatic pressure induced by the far more powerful con- 
tractions of the circular and longitudinal muscles. I cannot, 
therefore, believe that — in Urochseta at any rate — there are 
any pores which put the haemal system into communication 
with the surrounding medium; and in the meantime their 
resemblance to the integumental blood -capillaries of Limno- 
drilus is worthy of note. 
§ Excretory System. 
The nephridial system of Urochseta has been partly de- 
scribed by Perrier (22) ; according to his account it consists 
of (1) a large gland, termed “ glande h mucosite,” occupying 
the first few segments of the body ; (2) a series of “ segmental 
organs/’ one pair to each segment ; (3) a series of remarkable 
structures only developed in the posterior region of the body, 
where they are present to the number of a pair to each seg- 
ment; they coexist in these segments with the ordinary 
nephridia. I shall consider severally these different organs, 
which together constitute the excretory system. 
Mucous Gland. — The mucous gland is figured and de- 
scribed by Perrier as consisting of a tuft of long, much coiled 
glandular tubules, which ultimately unite and open on to the 
exterior by a long muscular duct. The orifices are situated 
upon the first segment, and are each surrounded by a group 
of muscular fibrils forming a sphincter. I have already (4) 
