170 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
ment divides into a supramuscular branch that continues the course 
above the muscles, and an inframuscular branch that pierces them 
and runs caudad beneath them in the position of a ventral abdominal 
artery. 
The blood vessels in the larvae can only be studied satisfactorily 
from serial sections and hence there are annoying gaps in my record. 
For the arteries are scarcely traceable unless distended with blood, 
and only a few specimens of any stage will chance to show the 
desired condition. As a rule, however, all the dorsal vessels were 
equally well preserved and much could be learned from a single 
s])ecimen, but ventrally the shrinkage of the integument against the 
ganglia obliterated the arteries to a greater or less degree. These 
and other causes also, prevented a study of the venous sinuses. 
The only artery passing cephalad from the heart in the earlier 
zoea stages is the anterior aorta, and it extends to the base of the 
rostrum, lying close beneath the dorsal wall of the cephalothorax. 
In the fourth stage its anterior end becomes deflected over the sur¬ 
face of the supra-oesophageal ganglion. No structure which sug¬ 
gested a cephalothoracic sac similar to that described for the zoea of 
Palaemonetes (Allen, ’ 93 ) was found at any stage. A sternal artery 
is present at all stages and passes down in its adult relations to the 
thoracic ganglia, between the fiber masses for the third and fourth 
pairs of limbs (pi. 7, fig. 29, st a ). The antennary arteries are first 
found in the fourth zoea and as they are not invariably present, they 
probably arise during the period. They diverge strongly and give 
off a branch to the stomach. Their ultimate distribution, however, 
could not be determined for the different stages. The hepatic 
arteries first appear during the glaucothoe stage after the livers 
have shifted to the abdomen. There is no trace of them in younger 
specimens even when the preservation of the heart and adjacent 
parts is perfect. 
The deferred development of the hepatic arteries can scarcely be 
regarded as correlated with the reduced function of these vessels 
in the adult crab, although at first this might seem probable. For, 
although among Decapods it is usual (Claus, ’ 84 ) for these arteries to 
be present throughout the larval period, this is not an invariable rule. 
The Thalassinid, Nauslionia (M. T. Thompson, : 03 ), has only anten¬ 
nary arteries and aorta forward from the heart during the zoea and 
mysis phases. Claus’s figures in his monograph on the circulation in 
