364 KANSAS UNIVERSITY SCIENCE BULLETIN. 



only diagrammatic. I was not able to obtain his paper. 

 Minot^^ made a histologic study of the grasshopper but did not 

 give much attention to the circulatory system. His paper con- 

 tains quite a complete bibliography of work done on the insects 

 prior to his publication. 



As is described for most insects, I found the pulsating tube 

 to end blindly in the last abdominal segment and the pulsa- 

 tions to extend forward. This was proven by exposing the 

 heart along its whole extent, but leaving it intact in the chitin, 

 and then placing a few drops of Ringer's solution colored with 

 neutral red on the posterior portion. Particles of the red were 

 taken into the heart and carried forward as far as the meso- 

 thorax. The contractions did not seem strong enough to force 

 them any further. This experiment confirms the opinion that 

 the blood enters the heart through lateral slits or valves. 

 There is probably a pair of these valves for each segment, al- 

 though microscopical sections did not reveal any definite valv- 

 ular structures. A few sections gave evidence of folds in the 

 tube, which were probably the valves. 



Figure 1, plate XXXVII, represents the heart in position as 

 it was usually exposed for experimentation. As will be seen, 

 the tube itself shows very little variations in size throughout 

 its whole extent. There is a slight enlargement at each seg- 

 ment, an enlargement in the metathorax, and also one in the 

 mesothorax. In the prothorax it becomes smaller and extends 

 \v [^ as a delicate tube, quite free from surrounding tissue or peri- 

 ^'•^w. ' cardial cells, into the head-cavity, where it is lost under a 

 large air-sac just back of the eyes. 



No other pulsating tube can be detected in any part of the 

 body, even by the aid of the microscope: It is very probable 

 that this anterior tube, or aorta, empties its fluid into the body- 

 cavity, and by means of the respiratory movements, perhaps, 

 and the pulsating sinuses, both ventral and dorsal, the blood 

 finds its way back to the posterior part of the body, where it 

 again enters through the valves of the heart and is propelled 

 forward. Owing to the extensive system of tracheal tubes and 

 air-sacs, located all over the body, it is probable that the blood 

 never becomes very venous, and the heart's chief function is 

 therefore to keep this fluid in motion and the tissues well 

 bathed with it. 



That the heart contraction is not dependent upon extrinsic 



15. Minot, C. S., Extracted from the second report of the U. S. Entomological 

 Commission, 1880, p. 196. 



