ORGANS OF SECRETION . 43 



"the manner in which the bee performs her incubatory office is 

 by placing herself upon the cell of a nymph (pupa) that is 

 soon to be developed, and then beginning to respire at first 

 very gradually. In a short time the respirations become more 

 and more frequent, until at length they are increased to one 

 hundred and twenty, or one hundred and thirty per minute. 

 The body of the insect soon becomes of a high temperature, 

 and, on close inspection, is often found to be bathed with per- 

 spiration. When this is the case the temperature of the insect 

 soon becomes reduced, and the insect leaves the cell, and an- 

 other bee almost immediately takes her place. When respira- 

 tion is performed less violently, and consequently less heat is 

 evolved, the same bee will often continue on a cell for many 

 hours in succession. This extreme amount of heat was evolved 

 entirely by an act of the will in accelerating the respiratory ef- 

 forts, a strong indication of the relation which subsists between 

 the function of respiration and the development of animal heat." 



Organs of Secretion. The urinary vessels, or what is 

 equivalent to the kidneys of the higher animals, consist in In- 

 sects of several loug tubes which empty by one or two common 

 secretory ducts into the posterior or "pyloric" extremity of 

 the stomach. There are also odoriferous glands, analogous to 

 the cutaneous glands of vertebrates. The liquid poured out is 

 usually offensive, and it is used as a means of defence. The 

 Bees, Wasps, Gall-flies, etc., and Scorpions, have a poison-sac 

 (Fig. 54^7) developed in the tip of the abdomen. The bite of 

 the Mosquito, the Horse-fly, and Bed-bug is thought by New- 

 port to be due to the simple act of thrusting their lancet-like 

 jaws through the skin, and it is not known that these and 

 other insects which bite severely eject any poison into the 

 wound. But in the spiders a minute drop of poison exudes from 

 an orifice at the end of the mandibles, " which spreads over the 

 whole wound at the instant it is inflicted." This poison is 

 secreted by a gland lodged in the cephalo-thorax, and which 

 is thought by Audouin to correspond in position to the salivary 

 apparatus and the silk glands of the Winged Insects. 



Organs op Generation. We have already described the 

 external parts. Tlie internal parts of the male insect consist, 



