191 
of the Carapace in the Decapod Crustacea . 
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 lacunas of the body-cavity, (2) of 
a branchial system in which the blood from the lacunae, after 
being arterialized, circulates in the direction of the heart, 
and is eventually poured into the pericardial chamber by 
which the latter is surrounded. 
Huxley reproduces these ideas in his work on the Crayfish, 
and adds that the pericardial sinus is perhaps partially occu- 
pied u by some blood which has not passed through the 
branchiae, though this is doubtful ” *. Claus, 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 lacunae 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 u 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 ” j\ 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 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 Mysis% , 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 ( Astacus fluviatilis ), on species of Pa- 
gurus (Eupagurus Bernfiardus , E . Prideauocii) , on Dromia 
( Dromia vulgaris) , on aquatic crabs ( Platycarcinus pagurus y 
* Huxley, ‘ The Crayfish ; an Introduction to the Study of Zoology,’ 
p. 56 (1880). 
t Claus, ‘*Zur Kenntniss der Kreisiaufsorgane der Schizopoden und 
Decapoden,” Arbeiten aus dem Zool. Instit. d. Univ. Wien, Bd. v. p. 40 
(1884). 
X Delage, “ Circulation et respiration chez les Crustacea Schizopodes 
( Mym)” Arch. Zool. Exp. 2 e serie, t. i. (1883). 
