68 GENERAL BIOLOGY. 



B. ANATOMY. 



I. Circulatory System. 



Gut ivith strong scissors through the two branchio- 

 cardiac grooves and transversely through the 

 cervical groove (taking great care not to cut 

 through the skin beneath) and remove the isolated 

 part of the carapace. 

 Note: 



The skin, colored by red pigment. 

 Cut through the body -wall by a shalloiu cut in the 

 median line and a transverse cut at each end of 

 the median cut. Turn aside the flaps, thus open- 

 ing the pericardial sinus and exposing : 



1. The heart : pentagonal and slightly yellowish, 



lying in the median line. 

 Find delicate strands of muscle that pass 



from the angles of the heart to the wall of 



the pericardial sinus. 

 The heart receives blood from the pericardial 



sinus through three pairs of valve-like 



openings, ostia : 



(a) A dorsal pair : visible now. 



(b) A lateral pair : better seen at a later 



stage (B. I. 2. (e)). 



(c) A ventral pair : better seen at a later stage. 



2. Arteries : arising from the heart. (These are 



extremely delicate and must be looked for 

 with great care.) 

 From the anterior region of the heart : 



