Xxxii INTRODUCTION. 



CIRCULATION. 



The circulatory system in the Amphipoda differs very 

 importantly from that of the Isopoda. According to some 

 researches of Professor Wagner * on the genus Porcellio, 

 there exists a well-developed arterial system in the 

 Isopoda. To establish this he adopted the method that 

 was first shown to be practicable by M. Emile Blanchard, 

 and which has since been successfully pursued by M. 

 Kowalewsky on Idotea. A mixture of glycerine and 

 water coloured with carmine injected through the heart 

 into the circulatory system, demonstrates the existence 

 of distinct vessels for the passage of the nutritive fluid. 

 The greatest amount of arterial development, as might 

 have been anticipated, is found to exist in the cephalic, 

 branchial, and generative regions, which the author 

 illustrates by diagrammatical figures. In the Amphipoda, 

 the heart is situated in the dorsal region of the pereion, 

 reaching from the posterior extremity of the first segment 

 to the posterior of the fifth. It is a long, simple, sack-like 

 vessel, consisting of elastic fibrous walls, possessing more 

 the features of a great arterial vessel than that of a true 

 heart. The blood corpuscles pass posteriorly from the 

 pulsating heart through the entire length of the animal 

 immediately above the alimentary canal, and the great 

 venous course returns along the dorsal surface, probably 

 on each side, until it reaches the last segment of the 

 pereion, where it dips to the ventral surface and enters 

 into the branchial sacs, where it passes down the anterior 

 margin and up the posterior, then direct to the heart, 

 which it enters by three lateral pulsating oblique aper- 

 tures. 



The heart of the Isopoda is situated within the dorsal 

 surface of the pleon, except in Tanais> and probably 



* Ann. des Sc. Nat. p. 37, vol. iv., 1865. 



