CRUSTACEA. 179 



The numerous experiments of Audouin and Milne Edwards * on 

 the circulation of the Crustacea, and the apparently favourable cir- 

 cumstances under which they were made, have very generally been 

 regarded as conclusive of the accuracy of their explanation of that 

 important function in the present class. According to these physio- 

 logists no other than the two great branchial veins terminate in the 

 heart, and, consequently, only pure aerated or arterial blood is pro- 

 pelled by it over the general system : the circulation is, in fact, the 

 same as in the Gasteropodous Mollusca : the ventricle is exclusively 

 systemic, and is provided with only two venous apertures. Four 

 such apertures are described and figured by Dr. Lund on the dorsal 

 surface of the heart, but these are regarded by Audouin and Ed- 

 wards as depressions merely between the muscular fasciculi, having no 

 communication with the ventricular cavity. 



I have tested the conflicting evidence of these observers by dissec- 

 tion of the heart in the lobster ; and you will perceive by this prepa- 

 ration -|- that it is more complicated than even the Danish Naturalist 

 supposed, and fully bears out the opinion of Hunter in regard to the 

 mixed nature of the circulation in the Crustacea. 



Fig. 91. shows the heart laid open on the ventral aspect ; by ex- 

 posing its cavity from this side, it was read- 

 ily determined whether the exterior de- 

 pression on the dorsal surface did or did 

 not lead into the cavity. On either side of 

 the anterior depression from which the two 

 antennal(/) and the ophthalmic (^) arteries 

 arise, there is a large oblique fissure, guarded 

 by a pair of semilunar valves. The vein^ 

 which terminates by each of these orifices, 

 is an extended, irregular, and extremely 

 flattened sinus, lying above the heart, and 

 between it and the lining membrane of 

 AstacusLrinus. ^^^ ^^^^11, communicating anteriorly with a 



similar broad irregular flattened sinus, 

 which occupies a similar situation above the stomach, and receiving 

 posteriorly the blood from a series of flat and expanded sinuses which 

 correspond to each segment of the tail. There are two similar 

 openings at the sides of the ventricle, posterior to the preceding, 

 which conduct the blood from lateral sinuses into the heart : these 

 orifices, indicated by the bristles (c, c), have each a pair of semilunar 

 valves. The arterial blood, returned from the branchiae, enters the 



* Hist. Nat. des Crustaces. 1829 t No. 898. A. 



N 2 



