47 



extend spirally and give to tracheae their characteristic, 

 transversely striated appearance. If a piece of one of the 

 larger tracheae be pulled apart the intima will tear between 

 the folds of the spiral thickening, and the latter will uncoil 

 from within the trachea like a thread. These spiral thicken- 

 ings are termed ice/iidia (Greek, little bands). In some insects 

 there are several, parallel thickenings of the intima, so that, 

 when an attempt is made to uncoil the tsenidia, a ribbon-like 

 band is produced, which is composed of several parallel taenidia. 



Make a preparation and a drawing illustrating the appear- 

 ance of a trachea of Corydalis^ with the taenidia partially 

 uncoiled. 



The heart and the aorta. — Read, the account of the 

 blood-vessels in Coinstock's Manual for the Study of Insects, 

 pp. 71, 72. 



In Corydalis the dorsal blood-vessel extends from the 

 eighth, abdominal segment to the brain. It is a slender tube, 

 widest in the region of the fourth and fifth abdominal seg- 

 ments. That part of it which lies in the abdomen is the 

 heart ; the more slender portion which traverses the thorax 

 and extends into the head is the aorta. 



The cephalic end of the aorta is attached to the brain, and 

 is trumpet-shaped except that the ventral wall of it is split. 

 In this way a V-shaped opening is formed, through which 

 the blood flows out, into the cavity of the head. 



Make a drawing representing the outline of the heart and 

 the aorta. 



The valves of the heart and of the aorta. — Usually it is very diffi- 

 cult to determine the position and form of the valves in the dorsal blood- 

 vessel in specimens preserved in chloral hydrate solution ; for a study of 

 these valves specimens which have been prepared especially for this pur- 

 pose are necessary. On this account this part of the subject may be omit- 

 ted by students taking a brief course in entomology. For the sake of 

 others the following method of study is indicated : 



