THE PULSE OF INSECTS 



411 



sopa, "used every endeavor to discover, if possible, whether the blood has proper 

 vessels, or only occupied the internal cavities of the canals ; and that he is con- 

 vinced that the latter is the case, as he could frequently perceive the particles 

 not only surrounding all parts of the tracheae, and occupying the whole of the 

 internal diameter of the canals, but that it frequently happens that globules 

 experienced a momentary stoppage in their progress, occasioned by their friction 

 against the curved surface of the tracheae, which sometimes gave them a rotatory 

 motion." 



Moseley found, owing to the large size and number of the corpuscles, that the 

 circulation of the blood in the wings of insects is most easily observed in the 

 cockroach, especially the hind wings. As seen in Moseley's figure, the blood 

 flows outward from the body through the larger veins (I and II) of the front 

 edge of the wings, which he calls the main arteries of the wings, and more 

 generally returns to the body through the veins in the middle of the wing ; the 

 blood also flows out from the body through the inner longitudinal veins (those 

 behind vein IV), and the blood is also 

 seen to flow through some of the 

 small cross-veins. Fig. 383 shows one 

 of the main trunks during active cir- 

 culation. The corpuscles change their 

 form readily, "the spindle-shaped ones 

 doubling up in order to pass crossways 

 through a narrow aperture. ... In the 

 irregularly formed corpuscles, which 

 seem to represent leucocytes, amoeboid 

 movements were observed. . . . Cor- 

 puscles pass freely above and under 

 the tracheae, showing that these latter 

 lie free in the vessels." The hypo- 

 dermis lining the vessels is best seen 

 in the small transverse veins. 



The pulse or heart-beat of 

 insects varies in rapidity in dif- 

 ferent insects, rising at times of 



excitement, as Newport noticed FIG. 383. - Parts of a vein of the cockroach, 

 4 .7 7 u-/ioi, showing the nerve (n) by the side of the trachea 



in AntllOphora retUSa, tO 14 J beats (tr ) - c , Wood corpuscles.- After Moseley. 



in a minute. 



When an insect, as, for example, a tineid caterpillar, has been en- 

 closed in a tight box for a day or more, the pulsations of the heart 

 are very languid and slow, but soon, on giving it air, the pulsations 

 will, as we have observed, rise in frequency to about 60 a minute. 

 Herold observed 30 to 40 in a minute in a fully-grown silkworm, 

 and from 46 to 48 in a much younger one. Suckow observed but 30 

 a minute in a full-grown caterpillar of Gastropacha pint, and 18 only 

 in its pupa. 



In a series of observations made by Newport on Sphinx lignstri from the 

 fourth day after hatching from the egg until the perfect insect was developed, 

 he found that before the larva cast its first skin the mean number of pulsations, 



