CIRCULATION OF THE BLOOD 409 



bodies mostly serve as the material for the formation of the blood-building 

 tissues, in caterpillars the tracheal matrix also, and, in dipterous larvae, the 

 hypodermis serve this purpose. (Caesar Schaeffer in Kolbe. See also Wielo- 

 wiejski, Ueber das Blutgewebe.) 



Other substances occur in the blood of insects. Landois (1864) demonstrated 

 the existence of egg albumen, globulin, fibrin, and iron in the blood of caterpil- 

 lars. Poulton found that the blood of caterpillars often contained chlorophyll 

 and xanthophyll derived from their food plants. A. G. Mayer has recently 

 found that the blood (haemolymph) of the pupae of Saturniidae (Callosamia pro- 

 methea) contains egg albumin, globulin, fibrin, xanthophyll, and orthophos- 

 phoric acid, and Oenslager has determined that iron, potassium, and sodium are 

 also present. (Mayer.) 



c. The circulation of the blood 



Every part of the body and its appendages is bathed by the blood, 

 which circulates in the wings of insects freshly emerged from the 

 nymph or pupal state, and even courses through the scales of Lepi- 

 doptera, as discovered by Jaeger (Isis, 1837). 



In describing the mechanism of the heart we have already con- 

 sidered in a general way the mode of circulation of the blood. 



The heart pumping the blood into the aorta, the nutritive fluid 

 passes out and returns along each side of the body ; distinct, smaller 

 streams passing into the antennae, the legs, wings (of certain insects), 

 and into the abdominal appendages when they are present. All 

 this may readily be observed in transparent aquatic insects, such as 

 larval Ephemerae, dragon-flies, etc., kept alive for the purpose under 

 the microscope in the animalcule box. 



Carus, in 1827, first discovered the fact of a complete circulation 

 of the blood, in the larva of Ephemera. He saw the blood issuing in 

 several streams from the end of the aorta in the head and returning 

 in currents which entered the base of the antennae and limbs in which 

 it formed loops, and then flowing into the abdomen, entered the pos- 

 terior end of the heart. Wagner (Isis, 1832) confirmed these obser- 

 vations, adding one of his own, that the blood flows backward in 

 two venous currents, one at the sides of the body and intestine, and 

 the other alongside of the heart itself, and that the blood not only 

 entered at the end of the heart, but also at the sides of each seg- 

 ment, at the position of the valves discovered by Straus-Diirckheim. 



Newport maintains that the course of the blood is in any part of 

 the body, as well as in the wings, almost invariably in immediate 

 connection with the course of the tracheae, for the reason that " the 

 currents of blood in the body of an insect are often in the vicinity 

 of the great tracheal vessels, both in their longitudinal and trans- 

 verse direction across the segments." 



