170 W. B. BENHAM. 



he remarks (p. 115) that important modifications occur in the 

 internal vessels, to which " I shall not now allude further." 



Beddard states, on p. 549 of his memoir on Libyodrilus, 

 that ^' the plexus of blood-vessels on the wall of the oesophagus, 

 which lie immediately below the epidermis {sic), was nowhere 

 a sinus, although the individual vessels were so close together 

 as to give this appearance" — his figures represent a sinus. 



From my own observations, I find that Criodrilus is 

 provided with a sinus similar to that of Sparganophilus, 

 which, like it, is replaced anteriorly by a plexus ; but in the 

 hinder part of the oesophageal region certain portions of the 

 plexus are wider than the rest, so that in section it looks as 

 if one had sections of separate vessels ; but closer examination 

 of several sections shows that there is really a continuous 

 sinus. Wiren has described in Arenicola a very similar 

 condition of intestinal vascular system, which had, up to his 

 time, been considered and represented as a network. 



I find, amongst the Lumbricidse, another genus with a dis- 

 tinct perienteric sinus, namely, AUurus; this I find in sec- 

 tions, and by removing a portion of the intestinal wall. 



In Dendrobsena rubida, however, I am unable to satisfy 

 myself as to whether a sinus or a network exists, though I am 

 inclined to believe the latter. 



The condition of a perienteric sinus is, by some zoologists, 

 regarded as more primitive than that of a network, and this 

 opinion appears to rest on the suggestion that the vascular sys- 

 tem is directly derived from the blastoccel or segmentation 

 cavity. What amount of embryological evidence exists scarcely 

 sufl&ces to settle the matter in regard to Oligochastes. AVilson 

 (' Journ. of Morphology,' iii, p. 408), in his memoir on the "Em- 

 bryology of the Earthworm," states that the first vessel to appear 

 is the subintestinal ; this is at first without proper walls, and 

 occupies a place between hypoblast and splanchnic mesoblast ; 

 but here and there a cell may be detected in its dorsal wall, 

 and these gradually increase in number till the vessel is pro- 

 vided with its own proper wall. He was unable, after the 

 most careful examination, to detect the precise origin of these 



