THE ORGANS OF CIRCULATION AND RESPIRATION. 141 



Circulation of the Cockroach. 



The pulsations of the heart are rhythmical and usually 

 frequent, the number of beats in a given time varying with the 

 species, the age, and especially with the degree of activity or 

 excitement of the Insect observed.* 



Cornelius ( watched the pulsations in a white Cockroach 

 immediately after its change of skin, and reckoned them at 

 eighty per minute ; but he remarks that the Insect was restless, 

 and that the beats were probably accelerated in consequence. 



In the living Insect a wave of contraction passes rapidly 

 along the heart from behind forwards ; and the blood may 

 under favourable circumstances be seen to flow in a steady, 

 backward stream along the pericardial sinus, to enter the lateral 

 aperture of the heart. The peristaltic movement of the dorsal 

 vessel may often be observed to set in at the hinder end of the 

 tube before the preceding wave has reached the aorta. 



From the heart a slender tube (the aorta) passes forward to 

 the head. It lies upon the dorsal surface of the oesophagus, 

 which it accompanies as far as the supra-oesophageal ganglia. 

 In many Insects the thoracic portion of the dorsal vessel is 

 greatly narrowed and non-valvular, forming the aorta of most 

 writers on Insect Anatomy. The aorta often dips downward 

 near its origin, but in the Cockroach the thoracic portion of the 

 vessel keeps nearly the same level as the abdominal. It gives 

 off no lateral branches, but suddenly ends immediately in front 

 of the cesophageal ring in a trumpet-shaped orifice, f by which 

 the blood passes at once into a lacunar system which occupies 

 the perivisceral space. Here the blood bathes the digestive and 

 reproductive organs, receives the products of digestion, which 

 are not transmitted by lacteals, but discharged at once into the 

 blood ; here, too, it gives up its urates to the excretory tubules, 

 and its superfluous fats to the finely-divided lobules of the fat- 

 body. The form of the various appendages of the alimentary 



* Newport, in Todcl's Cyclopaedia of Anatomy and Physiology, Art. Insecta, 

 pp. 981-2. 



T Beitr. zur niiheren Kenntniss von Periplaneta orientalis, p. 19. 



J The termination of the aorta has been described by Newport, in Sphinx (Phil. 

 Trans., 1832, Pt. I.,p. 385) Vanessa, Meloe, Bla})$ and Timarcha. (Todd's Cycl., 

 Art. "Insecta," p. 978.) 



