INTESTINAL RESPIRATION IN ANNELIDS. 783 



muscular layer, which membrane and cells he derives from the entoderm, within which 

 the original development of the vascular system took place. And while Lang considers 

 the cardiac body of certain Enchytrpeidse, the valves and the blood-corpuscles — i.e. 

 cells or cell-aogregates which occur within the lumen of the vessels, — as ingrowths from 

 outside the blood-vessel, Ve.tdovsky holds that these are special developments of the 

 cells of the entodermal linine; membrane.* 



Vejdovsky's work, being entirely histological, has not so many points of contact 

 with mine as has Lancj's ; nevertheless, a reference to it was unavoidable, and will be 

 equally incumbent in the future on any writer who considers the origin of the vascular 

 system. It will sutfice here to draw attention to a few points of fundamental importance 

 with regard to which the views set forth in the present paper are in harmony with 

 those expressed or implied by Ve.tdovsky. These are— (l) the origin of the vascular 

 system as a space or system of spaces at the base of the layer of intestinal epithelium 

 (not necessarily within that layer) ; (2) the consequent importance of the recognition 

 of the perienteric plexus as the primitive constituent of the vascular system ; (3) the 

 derivation of the musculature of at least the chief vessels from the muscular coats of 

 the alimentary canal. 



A piiper by Freudweiler (18), who had not then seen Vf;.jdovsky's first contribution, 

 immediately succeeded the appearance of the latter ; the histological results of the 

 authoress are opposed to those of Vejdovsky. Ve.tdovsky upholds his former conclusions 

 in a second contribution (56) ; still more recently Sterltnu (52) also disagrees with 

 Vejdovsky's results. But since my work is purely from the side of physiology and 

 comparative anatomy, it does not fall within my province to discuss this aspect of the 

 matter further. 



II. INTESTINAL RESPIRATION IN POLYCHiETA. 

 I. Historical. 



In dealing with intestinal respiration in the Oligochseta, it was possible to compress 

 into a very small space all previous references to the subject. In the Polychaeta, on 

 the other hand, intestinal respiration, or, to speak more broadly, respiration through 

 the alimentary wall, is a well-recognised phenomenon ; and it may therefore serve a 

 useful purpose if, before detailing my own observations, I devote a separate section to 

 a summary account of previous contributions. 



Three modes are known in which respiration may take place through the lining 

 of the alimentary canal — (l) by the introduction of water or air through the mouth ; 

 (2) by the introduction of water through the anus into and along a ventral groove in 



* Vejdovsky's view with regard to the blood-corpuscles would be more exactly expressed by saying that he considers 

 thcni to be descended from isolated entodermal mesenchyme cells, while other similar mesenchyme cells gave rise to 

 the cells of the lining membrane. The blood-corjiuscles would thus be descended from the same source as the lining 

 cells, but not from those cells themselves (loc. rit., p. 162). 



TRANS. ROY. SOC. EDIN., VOL. XLIX. PART III. (NO. 14). 107 



