of the Carapace in the Decapod Crustacea. 191 



Krohn, and, above all, of H. Milne-Edwards, consists (1) of 

 an arterial system which conveys the blood directly from the 

 heart and pours it into the lacunte of the body-cavity, (2) of 

 a branchial system in which the blood from the lacunas, after 

 being arterialized, circulates in tlie direction of the heart, 

 and is eventually poured into the pericardial chamber by 

 whicli the latter is surrounded. 



Huxley reproduces these ideas in his work on the CrayHsh, 

 and adds that the pericardial sinus is perhaps partially occu- 

 pied " by some blood which has not passed through the 

 branchiae, though this is doubtful '^ *. Claus, in a recent 

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

 of the carapace always contains venous bloody derived it 

 may be from the lacunaj 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 this blood " certainly does not flow into 

 the branchial sinus for the purpose of passing through the 

 branchia?, but passes directly from the body-walls into the 

 pericardial sinus " t- The learned carcinologist appears to 

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

 who liolds the heart of the Decapod Crustacea to be an 

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

 ever, lie 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 larvae of Decapod Crustacea, 

 before the branchiae appear, have no other respiratory appa- 

 ratus than the membrane of the carapace, and must therefore 

 respire in the same manner as MijsisX, 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. 



Numerous experiments and a large number of injections 

 performed on crayfish {Asiacus Jluviatilis) ^ on species of Pa- 

 gurus {Eupagurus Bernhardus^ E. Prideauxii), on Dromia 

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



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

 p. 56 (1880). 



t Claus, '• Zur Keuutuiss der Kreisiaufsorgane der Schizopoden und 

 Decapoden," Arbeiten au3 deni Zool. Instit. d. Univ. Wien, Bd. v. p. 40 

 (1884). 



X Uelage, " Circulation et respiration chez les Crustacea Schizopodes 

 {Mysis);' Arch. Zool. Exp. 2« serie, t. i. (1883). 



