148 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



elements. The principal vessel supplying blood 

 to the ventral regions is the sternal artery (fig. 

 79) which in some Malacostraca arises from the 

 posteroventral surface of the heart, but in Penaeus 

 is a branch of the very rostral portion of the 

 dorsal abdominal artery. The sternal artery de- 

 scends directly ventrad past the gut and through 

 the ventral nerve cord between the ganglia of the 

 third and fourth ambulatory legs (figs. 76, 79). 

 Here, the artery divides into an anterior portion 

 running forward beneath the nerve cord in the 

 gnathothorax and a posterior piece which even- 

 tually enters the abdomen (figs. 36, 79, 81). 



VENTRAL THORACIC ARTERY 



The ventral thoracic (subneural) artery (figs. 

 36, 79) supplies blood to the gnathothoracic ap- 

 pendages (fig. 36) as it passes anteriorly. Slightly 

 rostrad of the nerve to the second maxilla, the 

 ventral thoracic artery bifurcates. The two 

 branches turn sharply laterad, sending branches 

 into the nerve cord in the region of the mandibu- 

 lar nerve and also into the anterior structures of 

 the ventral thorax. No connection between the 

 anterior branches of the ventral thoracic artery 

 and the lateral anterior artery has been found in 

 Penaeus. 



The portion of the ventral thoracic artery pos- 

 terior to the sternal junction gives off large 

 branches to the fourth and fifth walking legs and 

 the anterior ends of the anterior oblique muscles 

 (fig. 36). A small branch continues subneurally 

 to join other vessels beneath the first abdominal 

 ganglion. 



B. Appendicular Blood Vessels 



EYESTALK VASCULAR SUPPLY 



Figures 7 to 10 



Blood is pumped to the eyestalk through the 

 optic branch of the lateral anterior artery. Once 

 in the eyestalk the vessel, now known as the oculo- 

 motor artery, runs medially along the optic tract 

 and divides into several branches at the distal 

 end of the eyestalk. The most proximal branch 

 bifurcates on the dorsal surface of the optic tract 

 (figs. 7, 8), sending a short vessel to and appar- 

 ently through a small gland on the optic tract 

 here designated as the X-Organ of Hanstrom 

 (1948) and about which something has been said 

 in the section on the nervous system. A small 

 part of the arterial branch to the gland continues 



proximally along the dorsal surface of the optic 

 tract and has not been traced beyond the connec- 

 tive tissue of the basal segment of the eyestalk. 

 The larger part of the proximal oculomotor 

 branch runs distally into the distal optic gang- 

 lionic mass (figs. 7, 8). 



Distally, the oculomotor artery divides into two 

 large branches, one of which (figs. 8, 9) carries 

 blood into a highly branched, dendritic structure 

 embedded deeply among the optic ganglion cells 

 (fig. 9). The organ has been named the capillary 

 arbor (Young 1956), since it appears to distribute 

 blood to ganglionic cells. Nothing similar has 

 been found in the literature of the arthropod eye. 

 However, Professor Mayrat reminds me that he 

 has described (Mayrat 1956) a similar structure 

 in Praunus flexuosus (O. F. Miiller). 



The other, and most-distal oculomotor branch, 

 repeatedly divides to form a vascular plexus on 

 the medial surface of the eyestalk, just beneath 

 a pore to the exterior (figs. 9, 10). The pore is 

 designated as the anterior eyestalk pore. This 

 structure was first described by Hanstrom (1948) 

 as the eye papilla or sensory papilla and is shown 

 by him as having some kind of structural and 

 spatial relationships with the X-Organ in several 

 crustaceans. Mayrat (1956) also finds the X- 

 Organ near the eyestalk pore in Praunus. The 

 function of the anterior eyestalk pore is unknown. 



ANTENNULAR BLOOD SUPPLY 



Figure 14 



The blood vascular supply to the antennule is 

 comprised of a large branch of the antennal ar- 

 tery, which is in turn a branch of the lateral 

 anterior artery. The antennal branch enters the 

 antennule in the mesial region near the point of 

 entry of the antennular nerves. The antennular 

 artery courses anteriorly along the mesial side 

 of the antennule giving off small branches to mus- 

 cles and other structures and finally dividing to 

 supply the two flagella. The arterial branches 

 are seen to subdivide to form capillary beds 

 about the antennule. 



ANTENNAL BLOOD SUPPLY 



Figures 21, 79, 80 



The antenna receives its blood from the anten- 

 nal branch of the lateral anterior artery. The 

 vessel gives off branches in the region of the large 



