150 THE CRAYFISH. 



d. The alse 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^iwall running from the bases of 

 the gills, and converging to open into the aides 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 sotne 

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

 entering the pericardial sinus. 



B. The Reproductive System. 



Carefully remove the side-ivall 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 Jhoracic leg. Before the breeding 

 season it will be found filled with an opaque 

 white seminal mass. 



Treat a small piece according to directions on p. 75 ; cover, 

 and examine it with low and high potvers. 



iii. The spermatozoa are flattened spheroidal cells 



