XXxll INTRODUCTION. 
CIRCULATION. 
The circulatory system in the Amphipoda differs very 
importantly from that of the Jsopeda. 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 Jsopoda is situated within the dorsal 
surface of the pleon, except in Tanais, and probably 
* Ann. des Se. Nat. p. 37, vol. iv., 1865, 
