XXIV 



ON THE VASCULAR SYSTEM OF THE LOWER 

 ANNULOSA 



British Association Report 1854 {Pt. 2) /. 109 



Under the term Lower Annulosa the author included the Anne- 

 lida, the Echinodermata, the Trematoda, the Turbellaria, and the 

 Rotifera, — in all of which there exists a peculiar system of vessels 

 which have hitherto been universally regarded as a blood vascular 

 system. Without considering the view he was about to lay before 

 the Section to be fully demonstrated, the author said that he had to 

 offer very strong reasons for regarding the prevalent notion as 

 incorrect. The vascular system of the higher Annulosa and of the 

 Mollusca is in all cases a more or less specialised part of the common 

 cavity of the body. The fluid which it contains is a corpusculated 

 fluid ; the propulsive organ, if any special heart exist, is a contractile 

 sac, connected by valvular apertures with that common cavity. Now, 

 although it might be incorrect to say that the vascular system 

 of the lower Annelida is invariably distinguished by characters the 

 opposite of these, still there can be no question that, as a general 

 rule, such is the case ; and this circumstance is alone sufficient to 

 raise grave doubts as to the homology of the two systems. But these 

 doubts are greatly strengthened when we take into consideration 

 certain facts, which the author proceeded to lay before the Section. 

 In the Rotifera there is a system of vessels, consisting of a contractile 

 vesicle, opening externally, from which canals, containing long vibratile 

 cilia, pass into the body. In certain Distomata, such as Aspidogaster 

 conchicola, there is a system of vessels of essentially similar character ;, 

 but the principal canals — those lateral trunks which come off directly 

 from the contractile vesicle — present regular rhythmical contractions. 



