282 



COMPARATIVE ANATOMY. 



largo ventral sinus, placed at the- base of the gills (in the so-called 

 sternal canal). Each gill (In) receives a vessel from this sinus 



(branchial artery). From 

 the gills the blood passes 

 into the branchial veins 

 (vbr), six or seven of which 

 arise on either side of the 

 pericardial sinus, into which 

 they often open by funnel- 

 shaped mouths. 



The valves of the venous 

 ostia are to be regarded as 

 special differentiations of 

 the heart, which aid in 

 dividing it into separate 

 chambers when it is elon- 



a <r 



gated. 



The circulatory system 

 of the Poocilopoda combines 

 several of these different 



their 

 heart lies in a 



stages ; 



elongated 



per 



icardial 



sinus, from which it re- 

 ceives blood by seven pairs 

 of ostia; it does not only 

 o-ive off arterial trunks an- 

 teriorly and posteriorly, but 

 from the sides also, as do 

 the Stomapoda. 



§ 218. 



The circulatory organs 

 of the Tracheata very 

 much resemble the elon- 

 gated multi - camerate 

 hearts found in some Crus- 

 tacea; and the differences 

 are due rather to the de- 

 gree to which the vascular 

 system which passes from 

 the heart is developed. This 

 again is affected by its 

 relations to the respiratory 

 organs, for when they are 

 limited to a- small space the 

 blood-vessels are more perfectly developed, while when the respira- 

 tory oi'gans are distributed over the whole body the arteries arc less 

 well developed. The Protracheata appear to resemble them in this. 



Fig. 115. Diagram of the circulatory syslcm 

 of a Lobster, o Eye. tie Lateral antenna?. 

 ai Mesial antenna?. br Branchiae. c Heart. 

 pc Pericardium. ao Median anterior aorta. 

 mi Ilepatic artery, op Posterior artery of the 

 body, a Trunk of th e ventral artery. « y Anterior 

 ventral artery, v Ventral venous sinus, v br 

 Branchial veins. The arrows indicate the 

 direction of the current of blood. 



