350 ALFRED GIBBS BOURNE. 
forms the main trunk of the venous system in the posterior 
region of the body, while the latero-longitudinals form the 
main trunks in the anterior region, and they join together to 
open into the dorsal vessel or a pair or pairs of hearts. 
Megascolides appears to have no portal system, because, 
according to Spencer, the latero-longitudinals open into the 
dorsal vessel; but no subneural is present, and no mention is 
made of ventro-intestinal vessels; so that unless the blood’ 
carried outwards by ventro-tegumentary vessels is returned to 
the dorsal vessel by the dorso-tegumentary vessels, and blood 
is supplied to the intestinal wall by dorso-intestinal vessels 
and returned—where and how we do not know—I am at a loss 
to explain Spencer’s account. But I am not prepared to base 
any arguments upon it, as one might imagine from the account 
that there was a perpetual supply of blood to the various 
capillaries which never returned thence. = 
Other variations in the vascular system are of apparently less 
importance, e. g. a supra-intestinal vessel is present in some 
species of a genus and absent in others. 
With regard to the course of the blood, I have little to add 
to what I have already said with regard to Megascolex 
ceruleus and Moniligaster grandis. These two types 
cover, with slight variations, all cases which I expect exist, 
except a case where there is no portal system and no subneural 
vessel; in such a case—and, as Spencer’s description stands, 
Megascolides presents this arrangement—the dorso-tegu- 
mentary vessels may be the veins of the peripheral capillaries. 
I have again and again returned to the course taken by the 
blood in these vessels. I cannot help thinking that primitively 
they are efferent vessels, and that both they and the dorso- 
intestinal vessels bring blood to the dorsal vessel. In this case 
they can only have, in worms otherwise well provided with a 
venous system, the function suggested above for M. grandis 
of regulating the pressure in the peripheral capillaries, and 
have practically no flow in them in one direction or the other, 
In this case it would not be surprising, in cases where there is 
no portal system and no subneural vessel or other main venous 
