356 



THE LOCUST 



The fact that the blood has no part to play in respiration 

 probably accounts for the simple organization of the circulatoiy 

 system in the grasshopper and other Insecta. In the Carolina 

 locust, the heart is a slender pulsatile tube extending along the 

 dorsal mid-line in the abdomen (Fig. 178) and closely applied 

 to the skeleton. Ventral to the heart is the pericardial sinus, 



which is separated from the 

 general space of the hsemocoele 

 by a horizontal membrane called 

 the dia'phragm. The heart, like 

 that of other arthropods, pos- 

 sesses ostia, or paired openings 

 guarded by valves through which 

 the blood enters from the per- 

 icardium {cf. Fig. 156, p. 324, 

 and Fig. 159, p. 331). From 

 the heart the blood is driven 

 into the aorta, which is an 

 anterior prolongation extending 

 through the thorax to the head. 

 On leaving this aorta, the blood 

 enters the general cavity of the 

 haemocoele, just as it does from 

 the ends of the arteries in the 



^, „ ^. , . crayfish. Being thus continu- 



IiG. 179. — Diagram showing course , , ,. i . .i , • 



of circulation in larva of a dragon o^^^^y dehvered at the anterior 



fly, Ejrilheca. 

 The flow of the blood through the heart 



end of the body and drawn 

 into the heart in the dorsal region 



(h^ and aorta (a), and its course through of the abdomCn, the fluid of the 

 the haBmoc<Tples may be seen in the living i ■, i • i • ji 11 1 



animal as shown by the arrows. (After haemOCOele, whlch IS the blood, 



Kolbe, from Folsom, "Entomology," copy- circulates slowly thrOUgh the 

 right, 1906, by P. Blakiston's Son & Co., 1 1 <• .1 . • 1 ^^ 



reprinted by permission.) ^ody from the anterior to the 



posterior parts, and thence 

 passes dorsally to the pericardium where it again enters the heart 

 through the ostia (Fig. 179). Such a circulatory mechanism 

 is far less efficient than the closed system of vessels that occurs 

 in vertebrate animals and in annulates like the earthworm. It 

 is, however, effective enough for insects, with their special mode 

 of respiration. What may be called the blood of the grass- 

 hopper is, therefore, the colorless fluid contained in all the spaces 



