GENERAL STRUCTURE. 37 



heat it may be necessary to maintain so as to best 

 suit the condition of the brood chamber. 



Although insects, and bees in the number, have no 

 general system of blood vessels, as I just now said, 

 they still have a beautiful apparatus by which their 

 fluids are continually carried round and made in 

 purity to visit for nourishment and renewal every 

 part of the body. Their heart, or blood pump, is 

 called, on account of its position, the dorsal vessel, 

 for it runs as a complex tube (dv, Plate I., and Fig. 

 8) along the back, almost immediately beneath the 

 external skeleton. This heart may be seen in action 

 in almost every caterpillar, where the opening and 

 closing of the ventricles, as they are called (v, Plate I.), 

 can be watched through the semi-transparent skin. 

 If we are fortunate enough to possess a microscope, 

 we may very easily see the pulsations far more 

 beautifully in the tiniest of the larvae. Remove 

 from its cell with a blunt needle the smallest to 

 be found, place it on a glass slip, add a drop of 

 water, and, with gentleness, a thin cover glass, 

 when the transparent larva will show, with an inch 

 objective, many wonders beside its spiracles and 

 tracheae, digestive tube, and nerve system, with the 

 dorsal vessel continuing for some time to gently 

 pulsate. Without a microscope, a little manual 

 dexterity will make the movements of the heart 

 visible in the adult bee. If one accidentally injured 

 is not at hand, a victim to science must be decapi- 

 tated, and then opened on the under side of the 

 abdomen, so as to remove the stomach and expose 

 the mere back shell seen from within, as Fig. 8 will 



