CRUSTACEA 



349 



233) a system of arteries interposes between the heart and the sinuses, 

 leaving the former by several vessels, which conduct the blood to the 

 organs. In the Eucarida (Euphausiacea and Decapoda) the heart is 

 shortened to a compact shape and has three pairs of ostia; in most of 



Fig. 232. Part of the left side of a late larva of the prawn Penaeus to show the 

 origin of the gills. Slightly magnified. After Claus. L^-L^, the first to fifth 

 legs; Mi-M^, the first to third maxiUipeds; la, 2a, 3a, ya, distal series of 

 rudiments, standing upon the coxopodites ; from these rudiments arise the 

 mastigobranchiae (see p. 408), and on the second maxilliped a podobranch also ; 

 16, 56, ic, 2C, 7c, members of two series of rudiments, standing where the 

 membrane of the joint between the coxopodite and the body will develop ; 

 from these respectively the anterior and posterior members of pairs of arthro- 

 branchiae arise ; i </, 5 J, 7 J, members of a fourth series of rudiments, standmg 

 on the basal parts (precoxae) of the limbs; from this series will arise the 

 pleurobranchiae, which, owing to the taking up of the precoxae into the body, 

 will stand on the side of the thorax. 



the Cladocera it is a sac (Fig. 244, h.) with only one pair. In the Cirri- 

 pedia and many of the Copepoda and Ostracoda the heart is absent 

 and the blood is kept in movement only by the movements of the body 

 and alimentary canal. In the parasitic copepod Lernanthropus and 



