130 THE PHYSIOLOGY OF THE COMMON CRAYFISH. 



and more elongated : the hinder median division lies 

 under the heart ; the anterior divisions are situated 

 between the heart behind, and the stomach and the liver 

 in front (figs. 5 and 12, t). From the point at which the 



Fig. 31. — Astacus flreviatilis. — The male reproductive organs ( x 2) ; 

 t, testis ; vd, vas deferens ; vd', aperture of vas deferens. 



three divisions join, proceed two ducts, which are termed 

 the vasa defer entia (fig. 31, vd). These are very narrow, 

 long, and make many coils before they reach the apertures 

 upon the bases of the hindermost pair of walking limbs, by 

 which they open externally (fig. 31, vd', and fig. 35, vd). 

 Both the ovary and the testis are very much larger 



