of the Larve of the Marine Crustacea. 9 
following an oblique line, which removes them from the median 
or ophthalmic artery, emit, in passing, a branch to the rudi- 
mentary czeca which represent the liver, and distribute them- 
selves at the base of the outer antenne. Lastly, the two re- 
maining arteries, at their issue from the arterial heart, are imme- 
diately reflexed downwards and lost beneath the liver and upon 
the sides of the stomach. These four arteries have their base 
furnished with a simple valve. 
The artery which springs from the posterior extremity is 
generally as voluminous as the anterior median artery. In the 
Phyllosomes it follows the dorsal line of the intestine for some 
distance, and then, on arriving at the level of the nervous 
ganglia of the third pair of true feet, it bends, passes on the left 
side of the intestinal tube, and divides into two trunks. One 
of these, which is very large, traverses the ganglionic chain, 
ascends as far as the mouth, and gives off to the right and left a 
branch to each of the ambulatory limbs and buccal appendages : 
it represents the sternal artery. The other, which is very slender, 
descends to the last abdominal segments, following the course of 
the intestine, and emits, in its course, a branch to the rudi- 
mentary buds which represent the fourth and fifth pairs of true 
legs. 
In the Zoéa-form larvee, in those of the Porcellane, Crangons, 
Lobsters, &c., the posterior artery, mstead of dividing only 
after passing a certain distance, bifurcates at its issue from the 
heart. One of its branches runs directly down to form the 
sternal artery, after having traversed the thoracic ganglionic 
mass at the same point as in the Phyllosomes; the other 
branch follows the intestine to its extremity, remaining of a 
considerable size throughout. This branch, which answers to 
the superior abdominal aorta of the adult Crustacea, presents, in 
the young Lobsters, a very remarkable peculiarity : on its course, 
at a distance from the heart and a little above the constriction 
which separates the intestine into the duodenum and rectum, it 
has a sort of sphincter or circular valve, which contracts abso- 
lutely in the same manner as the pupil of the eye of the cat. 
Its contractions, which occur at indeterminate periods, progres- 
sively and slowly, have the effect of obliterating, entirely or 
partially, the calibre of the artery, so as to suspend, for some 
seconds, the circulation in the postabdomen, or to moderate 
the flow of blood towards that region. This fact is so excep- 
tional that I cannot but call the attention of physiologists 
to it. 
All the arteries, whatever be their size, have their extremities 
bevelled, and terminate suddenly in a venous lacuna by an oval 
opening, usually a little dilated into a trumpet-shape. 
