of the Carapace in the Decapod Crustacea. 191 



Krohn, and, above all, of II. Milne-Edwards, eonsists (1) of 

 an arterial system whieh conveys the blood directly from the 

 heart ;ind ponrs it into the lacunar of the body-cavity, (2) of 

 a branchial sy.stem in which tiie blood from tlie lacnnie, after 

 bein<^ artcrializcd, circulates in the direction of the heart, 

 and is eventually poured into the pericardial chamber by 

 which tjie latter is siurouiuled. 



Huxley reproduces these ideas in his work on the Crayfish, 

 and adds that the jx-ricardial sinus is perhaps partially occu- 

 pied " by some blood which has not passed through the 

 branchiae, though this is doubtful " *. Glaus, in a recent 

 paper, is much more positive ; he states that the membrane 

 of the carapace always contains venous blood, derived it 

 may be from the lacuna3 of the body-cavity, it may be 

 from the arterial extremities of the tegumentary branches 

 of the lateral anterior arteries (antennary arteries), and he 

 justly observes that (his blood " certainly does not flow into 

 the branchial sinus for the purpose of passing through the 

 branchiae, but passes directly from the body- walls into the 

 pericardial sinus " f- The learned carcinologist appears to 

 make use of this fact to combat the opinion of Milne-Edwards, 

 who holds the heart of the Decapod Crustacea to be an 

 arterial heart in the sense that the Molluscan heart is; how- 

 ever, he merely formulates, without further details, the rule 

 quoted above, contenting himself with describing very 

 minutely the circulation in the carapace of the Phyllosoma- 

 stage of the larva of the lobster. 



Now, if we consider that the larva? of Decapod Crustacea, 

 before the branchia3 a})pcar, have no other respiratory appa- 

 ratus than the membrane of the carapace, and must therefore 

 respire in the same manner as J/y,sw + , we are forced to believe 

 that, in the absence of demonstrative proof, we cannot draw 

 conclusions from the larva as to the adult, and we ask our- 

 selves whether Milne-Edwards may not be right after all in 

 holding the Decapod heart to be exclusively arterial. 



Kumerous experiments and a large number of injections 

 performed on crayfish {Astacus fluviatiUs) ^ on species of Pa- 

 gurus {Eupagurus Bern/iardus, E. Prideauxii), on Dromia 

 {Dromia vulgaris) ^ on aquatic crabs (Platycarcinus pagurus^ 



* Huxley, ' The Crayfish ; an lutroductiou to the Study of Zoology,' 

 p. 56 (1880). 



t Clans, '• Zur Kenntniss der Kreislaufsorgaue der Schizopoden und 

 Decapoden," Arbeiten aus dem Zool. lustit. d. Univ. Wien, Bd. v. p. 40 

 (1884). 



X Delage, " Circulation et respiration chez les Crustacea Schizopodes 

 {Mysis)," Ai-ch. Zool. Exp. 2« s^rie, t. i. (1883). 



