142 THE COCKROACH: 



canal (salivary glands, cnccal tubes, and Malpighian tubules), as 

 well as of the testes, ovaries, and fat-body, is immediately con- 

 nected with the passive behaviour of the fluid upon which their 

 nutrition depends. Instead of being compact organs injected 

 at every pulsation by blood under pressure, they are diffuse, 

 tubular, or branched, so as to expose as large a surface as 

 possible to the sluggish stream in which they float. 



From the perivisceral space the blood enters the pericardial 

 sinus by the apertures in its floor, and returns thence by the 

 lateral inlets into the heart. 



No satisfactory injections of the circulatory channels can be 

 made in Insects, on account of the large lacunae, or cavities 

 without proper wall, which are interposed between the heart 

 and the extremities of the body. In the wings and other 

 transparent organs the blood has been seen to flow along 

 definite channels, which form a network, and resemble true 

 blood vessels in their arrangement. Whether they possess a 

 proper wall has not been ascertained. It is observed that in 

 such cases the course of the blood is generally forwards along 

 the anterior, and backwards along the posterior, side of the 

 appendage. The direction of the current is not, however, quite 

 constant, and the same cross branch may at different times 

 transmit blood in different directions.* 



Blood of the Cockroach. 



The blood of the Cockroach may be collected for examination 

 by cutting off one of the legs, and wiping the cut end with a 

 cover- slip. It abounds in large corpuscles, each of which 

 consists of a rounded nucleus invested by protoplasm. Amoeboid 

 movements may often be observed, and dividing corpuscles are 

 occasionally seen. Crystals may be obtained by evaporating a 

 drop of the blood without pressure ; they form radiating 

 clusters of pointed needles. The fresh-drawn blood is slightly 

 alkaline ; it is colourless in the Cockroach, but milky, greenish, 

 or reddish in some other Insects. The quantity varies greatly, 

 according to the nutrition of the individual : after a few days' 

 starvation, nearly all the blood is absorbed. Larvae contain much 

 more blood, in proportion to their weight, than other Insects. 



* Moseley, Q. J. Micr. Sci. (1871). 



