NEItILLA AN ARCHI ANNELID. 
407 
discussed below when treating’ of the body-cavity in the 
Archiannelids. 
The Vascular System. 
There is a simple vascular system, discovered and described 
by de Beauchamp ( 2 ). The blood being colourless and the 
walls of the vessels exceedingly delicate, it is very difficult to 
follow out the whole course of the system even in sections. 
As stated by de Beauchamp, there is a distinct peri-intestinal 
sinus extending over the dorsal and lateral surface of the 
intestine and hinder part of the stomach; from this sinus 
springs a median dorsal vessel, whicl/runs forwards above the 
oesophagus to tbe head, where it divides into two branches. 
These pass backwards and downwards on either side of the 
pharynx, 1 and join to a median ventral vessel running along 
below the stomach and intestine (figs. 30, 37, etc.). The 
vascular system is represented diagrammatically in fig. 20. 
Besides the vessels just mentioned there is in the female a 
laterad vessel not hitherto observed. It comes off the longi- 
tudinal ventral vessel in the sixth segment, and runs over 
the surface of the ovarian sac, appearing to end in the peri- 
intestinal sinus (figs. 28, 34). This vessel serves, no doubt, 
ns the indirect source of nourishment for the eggs which 
develop inside the sac. The walls of the blood-vessels are 
formed of contractile cells, probably in a single row. 
The Muscular System. 
The muscles have already been described by Miss 
Pereyaslawzewa and de Beauchamp ( 13 , 2 ). The system is 
but little developed, and consists essentially of two dorsal 
aud two ventral bands of longitudinal muscles running from 
head to tail. The dorsal are weaker and more flattened than 
the ventral (fig. 31). A few fibres more median are seen 
1 Salensky ( 19 ) denies the existence of the similar vessels described 
by me in Saccocirrus (8). There can be no doubt, however, of their 
presence. 
