312 



THE INVERTEBRATA 



into the sinuses of the head and thence through those of the trunk to 

 the pericardium, eddies from a main ventral sinus supplying the 

 limbs. In all other Crustacea, except the Stomatopoda, the heart, if 

 it be present, is in some degree shortened, and in the Malacostraca 



Fig. 22 1 . 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 ; M1-M3 , the first to third maxillipeds ; i a, 2 a, 30, ja, distal series of 

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

 mastigobranchiae (see p. 366), and on the third maxilliped a podobranch also ; 

 lb, 5b, I c, 2C, yc, 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 <i, 5 J, 7 d, members of a fourth series of rudiments, standing 

 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. 



(Fig. 222) 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 



