140 THE CRAYFISH 



Eemove the branchiostegite and the gills of the left side, 

 unless this has already been done. 



2. The branchiocardiac canals are a series of channels in 

 the body-wall, conveying blood from the gills to the 

 pericardial sinus. They can be seen through the 

 transparent body-wall running from the bases of 

 the gills, and converging to open into the sides of 

 the pericardial sinus. 



Cut a gill off close to its base, and blow into the cut end 

 of the efferent blood-vessel with a blowpipe, or inject some 

 coloured fluid into it, and observe the air or coloured fluid 

 entering the pericardial sinus. Pass a seeker along the canal 

 from below upwards. 



B. The Reproductive System. 



Carefully remove the side-wall of the thorax, and expose 

 the reproductive organs. 



a. In the male. 



i. The testis is a soft white body lying immediately 

 below the pericardial sinus, and extending 

 backwards a little beyond it. It consists 

 of a pair of anterior lobes, and a median 

 posterior lobe. 



ii. The vas deferens of each side is a long thick 

 convoluted tube, running from the junction of 

 the anterior and posterior lobes of the testis to 

 the external aperture on the coxopodite of the 

 last thoracic leg. Before the breeding season 

 it will be found filled with a chalky-white 

 opaque seminal mass. 



Tease a small piece of the mass in water or glycerine on 

 a slide ; cover, and examine it with low and high powers. 



iii. The spermatozoa are flattened spheroidal cells 

 from which radiate a number of stiff immobile 

 curved processes. 



