570 On the Uses of the Dorsal Vessel. [Ma¥, 



more singular, they continue to live after the dorsal vessel has been 

 entirely removed. 1 have seen the caterpillar of a sphinx atropos 

 breathe for six hours after I had removed the dorsal vessel. The 

 inspirations and expirations still continued, and air bubbles broke 

 from the ends of the trachete which had been cut at the removal of 

 the dorsal vessel. If this organ were a heart, how could insects 

 possibly live so long after being deprived of it. To be convinced of 

 the difference, let the heart be removed from those animals in 

 which it exists even in the least complicated state. Not one will 

 resist its loss, most of them will be dead before the removal can be 

 completed, i must observe, that after the removal of the dorsal 

 vessel, insects are no longer able to move about j but life notwith- 

 standing still continues. 



This intensity of life is found in all animals that have no centre 

 of action : other animals die very speedily. One would think there 

 ought not to be a great difference in this respect between the Jau- 

 cheurs and spiders, or between the scolopendras and scorpions, and 

 vet there is a very great one. The scorpions and spiders die almost 

 immediately after exposing their heart ; while insects live often six 

 or seven hours after removing the organs most essential to life. Yet 

 both have a nervous system composed of a series of ganglions ; but 

 the insects have no centre of circulation, or, which is the same 

 thing, they have no heart. 



We have seen the influence of the dorsal muscles on the con* 

 tractions of the dorsal vessel. As this influence might not be the 

 only one, 1 endeavoured to determine tliosc which might belong to 

 the tracheas and nerves. Before engaging in this new set of expe- 

 riments, I wished to determine whether by means of metallic ex- 

 citers 1 could render the contractions of the dorsal vessel more 

 frequent and stronger. \Vlien the two exciters were brought into 

 contact the insect exhibited symptoms of pain ; but the dorsal 

 vessel, instead of increasing in liveliness, beat always more and 

 more slowly. On continuing the contact of the wires of zinc and 

 copper between the membranes of the dorsal vessel, the humour 

 contained in this vessel gradually coagulated, end the contractions 

 ceased by degrees. Thus the galvanic agent in the present case 

 produces effects similar to the chemical, with this difference, that 

 it acts less rapidly. 



It might be concluded, a priori, that the trache.'e have a consi- 

 derable infljjfnce on the contractions of the dorsal vessel, on ac- 

 count of the great number of them which enttr it and constitute 

 one of its coats, and on account of the great influence of air on 

 the organs of iffsects. But grent difficulties I'-trvent us from de- 

 termining that influence; the most insurmountable of which is the 

 impossibility of separating the trachea? from the dorsal vessel : for, 

 without such a separation, we cannot judge of the influence whicli 

 they exert on its contractions. I have not been able to surmount 

 these difficulties in those insects which have tributary trachc.-e. 

 So that 1 can only depend upon one experiment, wliich succeeded 



