158 THE CRAYFISH. 



ii. From the hinder end of the heart arises the 

 large median dorsal abdominal artery, and 



immediately below this the large median 

 sternal artery, which latter can be better 

 seen at a later stage. 



d. The alae cordis are three pairs of fibrous bands 

 which hold the heart in position by connecting it 

 with the walls of the pericardial sinus. 



Remove the branchiostegite and turn down 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. 



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 behind it. It consists 

 of a pair of anterior lobes and a median 

 posterior lobe. 



ii. The vas deferens of each side is a long con- 

 voluted 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 



