of the Larva 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 caeca which represent the liver, and distribute them- 

 selves at the base of the outer antennse. 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. Iivthe 

 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 Zoea-form larvae, in those of the Porcellana, Crangons, 

 Lobsters, &c., the posterior artery, instead 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 eflfect 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. 



