12i 



ZOOLOGY 



Organs and Function of Circulation. — The circulatory 

 organs of the lobster, as of the higher Crustacea in general, are 



highly developed. The 

 heart is a long, muscular 

 tube lying in the dorsal 

 part of the thorax. It is 

 perforated by several pairs 

 of lateral openings through 

 which the body fluid passes 

 from the surrounchng body 

 cavity into the heart. 

 Thence it is forced do^^^l- 

 wards b^^ a great artery to 

 the ventral system, for- 

 ward to the digestive 

 glands, stomach, mouth- 

 parts, and eyes, and back- 

 wards to the muscles of the 

 abdomen. The blood that 

 enters these various organs 

 oozes out into the general 

 cavity of the body, streams 

 into the gills, and is thence 

 returned to the heart. 

 Thus the heart and the tis- 

 sues receive blood full of 

 oxygen acquired in the 

 gills. The Ijlood of the lobster is not colored red like our 

 blood because it lacks the blood corpuscles that give our blood 

 its color. Nevertheless the blood is able to absorb oxygen 

 from the water and give it off again to the tissues. 



Fig. 125. — Cross section of thorax of 

 Astacus fluviatilis of Europe, diagrani- 

 niatic. ahm, ventral muscles of the ab- 

 domen ; 6/, leg ; hni, main or ventral 

 nerve cord : rf, intestine ; dhvi, dorsal 

 muscles of abdomen ; ep, wall of thorax ; 

 h, heart ; k, gills ; kd, gill cover ; I, liver ; 

 ov, ovary ; j)c, space around heart ; .5(7, 

 sn, artery running along sternum ; vs, 

 ventral blood space. The arrows show 

 the direction of blood flow. From Lang, 

 "Comparative Anatomy." 



