INTERNAL ANATOMY. 39 



Moseley has figured and described the structure of the 

 veins and the circulation of the blood in the hind wing of 

 Blatta 07-ientalis. The latter can be observed in the wing 

 of this insect more clearly than in many others, owing to 

 the large size of the corpuscles and the absence of dark 

 pigment in the vessels. The so-called veins are blood- 

 vessels which have a thick lining of cells closely packed 

 together. After injecting these vessels with silver solu- 

 tion Moseley was unable to find any other lining than this 

 thick .stratum of cells. The principal blood-vessels, but 

 not the smaller transverse vessels, have tracheae running 

 through the middle like delicate filaments, and accompany- 

 ing each trachea is a nerve-fibre. The corpuscles change 

 their form readily, like those in the capillaries of a frog, and 

 in some amoeboid movements were observed. As the cor- 

 puscles have been seen to pass above and under the tra- 

 cheae, the latter must lie free in the vessels. ^ 



When a piece of the trachea of a locust is examined 

 microscopically, many short, spiral threads are seen imbed- 

 ded in the inner layer. Each thread passes around the 

 trachea a few times and then ends. These filaments are 

 elastic, and serve to keep the air-passages open like the 

 bands of cartilage in the trachea of man. Connected with 

 the tracheae are the air-sacs. Of these there are five pairs 

 on the dorsal surface of the abdomen (Fig. i6, q^-q"^) 

 underlying the inner layer of the skin. Two very large 

 ones are figured in the prothorax {q'), and a smaller pair 

 in the mesothorax {q'^). No less than fifty-three sacs 

 were counted by Packard in the head. Besides these, 

 many small sacs are buried among the muscles. 



When a living locust is held in the hand, the process 

 of breathing may be watched. The pliable connec- 

 tions between the rings and the more or less elastic 



1 Quart. Joiirn. Micro. Sa'., Vol, XL, 1871. 



