130 



THK PHYSIOLOGY OF THE COMMON CRAYFISH. 



and more elongated : the hinder median division lies 

 under the heart ; the anterior divisions are situated 

 hetween the heart hehind, and the stomach and the liver 

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



Fro. 31. — Astncus fnridfUis. — The male reproductive organs ( x 2) ; 

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



three divisions join, proceed two duets, which are termed 

 the vasa dcferentia (fig. 31, rd). These are very narrow, 

 long, and make many coils before thej" reach the apertures 

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

 wliich thej' open externally (fig. 31, vd', and fig. 35, vd). 

 Both the ovary and the testis are very much larger 



