CRUtiTACEA— BLOOD-VASCULAR SYSTEM 



365 



The heart of the Schhopoda, Decapoda, and Cumacea appears, as 

 contrasted with that of the Stomatopoda, extraordinarily shortened and 

 provided ^^^th very few ostia (2 to 3 pairs). It always lies in the 

 thorax and never stretches into the abdomen. This shortening 

 was evidently caused by the 

 localisation of the respiration in 

 the thoracic region (gills of the 

 thoracic feet, cephalothoraoic 

 shield as respiratory organ), and 

 by the more or less extensive "' 

 fusing of the thoracic segments. 



Among the Sckkopoda the 

 heart is still elongated in SirieUa, . 

 where it runs through nearly the '^ 

 whole thorax into the last thor- 

 acic segment. It is progressively ^, 

 shortened in My sis and Mysodopsis. 

 In Eupliausia it has the concen- 

 trated form of the Decapodan 

 heart, and has, like the latter, 

 3 pairs of ostia, one dorsal, one 

 lateral, and one ventral, while in 

 the other Schizopoda and in the 

 Zocea-larvce of the Decapoda, there 

 are but 2 pairs of ostia. 



The Circulatory system of 

 Astacus (Fig. 234, p. 338, and 

 Fig. 244) may be taken as an 

 example. The follomng vessels 

 rise out of the heart : (a) an- 

 teriorly the unpaired eephaUe 

 aorta, which supplies with its 

 rich branchings the brain and the 

 eyes, (b) Two anterior lateral 

 arteries (also called antennal 

 arteries). These give off branches to the stomach, the antennal glands, 

 the anterior and posterior antennae, and the cephalothoracic shield, 

 (c) The two hepatic arteries. These arise at the anterior and lower 

 edge of the heart and branch in the liver, (d) The sternal artery. 

 This arises from the lower and posterior end of the heart, which 

 is produced in the shape of a bulb, descends on the right or left 

 side of the intestine, passes between the longitudinal commissures 

 of the penultimate and ante-penultimate thoracic ganglia, to enter the 

 sub-neural vessel below the ventral chord. This must be considered 

 as a modified lateral artery of the heart (see Stomatopoda). (e) The 

 posterior aorta arises out of the posterior end of the heart, and runs 

 over the intestine backwards through the abdomen, giving off in each 



Fig. 244.— Transverse section througli the 

 cephalothorax of tlie Cray-fish in the region of 

 the heart, diagrammatic. M, brancliiostegite ; 

 Ic, gills ; kh, respiratory or branchial cavity ; ep, 

 lateral wall of the cephalothorax ; pc, pericardium ; 

 Jt, heart ; sa, sternal artery ; I, hepatopancreas ; d, 

 intestine ; dbmy ventral longitudinal muscles to 

 the abdomen ; dbm, dorsal longitudinal muscles to 

 the abdomen ; 6m, ventral chord ; sn, sub-neural 

 vessel ; &/, ambulatory foot ; vs, ventral sinus ; ov, 

 ovarium. The arrows give the direction of the 

 flow of blood (after Huxley and Plateau). 



