INSECTA. 383 



eiglit pairs of apertures ; in the stag-beetle {fig- 152) there arc six 

 pairs ; in the humble-bee five pairs ; in the phasma there is, according 

 to Miiller, only a single pair at the posterior chamber of the heart, 

 by which, in fact, in all Insects, the chief cuiTents of the blood 

 appear to enter the organ. As far as the head the blood is propelled 

 from the heart along a tubular aorta of the usual form ; but the 

 branches from this (b) would appear soon to lose themselves in the 

 generally difl'used sinuses. In the Myriapoda, however, the blood is 

 continued in a vessel along the dorsal aspect of the ventral nervous 

 chord ; but the traces of the true tubular vascular system are scanty 

 and obscure. 



The blood of Insects is usually a colourless fluid, sometimes 

 greenish or straw-coloured, rarely, as in the larvte of Chironomus, 

 approaching to a red colour : it contains flattened oat-shaped par- 

 ticles, which are sometimes tuberculated. 



Cuvier, misled by the anomalous diffused condition of the venous 

 system, supposed that there was no circulation of the blood in Insects ; 

 yet the dorsal vessel was too conspicuous a structure to be overlooked. 

 Such, however, was the authority of the great anatomist, that the 

 nature of the heart began to be doubted, and the strangest functions 

 to be attributed to it. Hunter, however, who was prepared to ap- 

 preciate the true state of the circulating system in insects, by his 

 discovery of the appi'oximatively diffused and irregular structure of 

 the veins in the Crustacea, has described in his Woi'k on the Blood * 

 all the leading characters of the circulation in Insects as it is recog- 

 nised by Comparative Physiologists of the present day. Pie says, 

 that, "As the lungs of the flying Insect are placed through the Avhole 

 body, the heart is more diffused, extending through the whole length 

 of the animal;" that "where the veins near the heart are large, there 

 is no auricle, as in the lobster and generally in insects ; " that " in 

 the winged Insects, which have but one heart, as, also, but one cir- 

 culation, there is this heart answering both purposes " (viz. the cor- 

 poreal and pulmonary circulations); and again, "with respect to its 

 use, it is, in the most simple kind of heart, to propel the blood through 

 the body, immediately from the veins, which blood is to receive its 

 purification in this passage, when the lungs are disposed throughout 

 the body, as in the flying Insect." In the note at p. 221. he alludes 

 to the animals in which the veins are entirely cellular ; and expresses 

 his idea more definitely in the following passage from his manuscript 

 Observations on Insects: — " Of the i-eins. The veins of the Insect 

 would appear to be simply the cellular membrane ; but they are 



* CCXLVIII. p. 220. el seq. 



