256 



MANUAL OF ELEMENTARY ZOOLOGY 



wide, and is prolonged in front and behind by non-contrac- 

 tile vessels— the ophthalmic and dorsal abdominal arteries. 

 We shall find in the cockroach a similar but longer heart. 



From the organs the blood passes into great sinuses which 

 surround them. The largest of these is the perivisceral 

 cavity, but there are also blood spaces in the limbs and 

 elsewhere. The blood from the limbs and a great part of 

 that from the perivisceral cavity is gathered up into a 

 sternal sinus, which lies in a tunnel formed by the endo- 



pt>r. 



Fig. 163. — The forepart of the body of a crayfish, viewed from the right- 

 hand side, with the legs and the branchiostegite cut away and the 

 gills displayed. 



arb., Arthrobranchiaj ; ep. y epipodite of the first maxilliped ; pbr. 

 plb., pleurobranchia ; scg., scaphognathite. 



podobranchu 



phragmal skeleton and contains the ventral nerve cord 

 and ventral thoracic artery. From this a series of afferent 

 branchial sinuses carries the blood to the gills, where it is 

 oxygenated. From the gills it passes by efferent branchial 

 sinuses to the pericardial sinus. Part of the blood from 

 around the stomach, however, passes on each side into the 

 space between the two sides of the fold of carapace which 

 forms the branchiostegite, and thence to the pericardial sinus 

 by a vessel which follows the hinder edge of the branchio- 

 stegite. It will be noted that the pericardial cavity of the 

 crayfish is a part of the hsemoccele and contains blood, un- 



