CB USTACEA BLOOD-VASCULAR ,s' 1>TJ7 



365 



This shortening 



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

 contrasted with that of the Stomatopoda, extraordinarily shortened and 

 provided Avith very feAv ostia (2 to 3 pairs). It ahvays lies in the 

 thorax and never stretches into the abdomen, 

 was evidently caused by the 

 localisation of the respiration in 

 the thoracic region (gills of the 

 thoracic feet, cephalothoracic 

 shield as respiratory organ), and 

 by the more or less extensive 

 fusing of the thoracic segments. 



Among the Schi:<>p<>da the 

 heart is still elongated in Siri<ll<i, 

 where it runs through nearly the 

 whole thorax into the last thor- 

 acic segment. It is progressively 

 shortened in Mysis 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, Avhile in 

 the other Schizopoda and in the 

 Zocea-larvce of the Decapoda, there 

 are but 2 pairs of ostia. 



The Circulatory system of 



/T -,. nf>i ooo i FIG. 244. Transverse section through the 



AstaCUS (Fig. 234, p. 33h, and cephalotnorax of the Cray-fish in the region of 



Fig. 244) may be taken as an the heart, diagrammatic, l-ii. branchiustegite ; 



example. The following Vessels k > S^', M, respiratory or branchial cavity: 



,. , , , , lateral wall of the cephalothorax ; pc, pericardium ; 



rise OUt 01 the heart: (a) an- 7ij heal . t . sa> s ternal artery; ?, hepatopaiinvas ; ,1, 



teriorly the Unpaired Cephalic intestine; abm, ventral longitudinal muscles t<> 



aorta, which supplies with its the abdomen; ^.dorsal longitudinal muscles to 



_ ' _ 1 i the abdomen; bm, ventral chord; sn, sub-neural 



rich branchings the braill and the vessel ; &/, ambulatory foot ; vs, ventral sinus ; or, 



eyes. (b) TWO anterior lateral ovarium. The arrows give the direction of the 



'/! n , T flow of blood (after Huxley and Plateau). 



arteries (also called antennal 



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

 the anterior and posterior antenna?, and the cephalothoracic shield. 

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

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

 This arises from the loAver 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 betAveen the longitudinal commissures 

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

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

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

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

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



