— 4Q 



the arrangement of the larger tracheae, and write a descrip- 

 tion of the same. 



The walls of the tracheae are 

 composed of three layers, which 

 correspond to the layers of the 

 ^/L, body-wall ; in fact the tracheae 

 are believed to be invaginations 

 of the body-wall. The continu- 

 ity of the membranes of the 

 tracheae and body-wall is shown 

 diagrammatically in Figure i. 

 It should be observed that it is 

 the inner layer of the wall of the 

 trachea that corresponds with 



Fig. i . — Section of trach ea and body- 

 wall, c cuticle; hy, hypodermis; the outer layer of the wall of the 



dm, basal membrane ; sp. spiral 

 thickening of the intima. bodv 



This inner layer of the wall of the trachea, the intirna, 

 like the cuticle is chitinous, and is shed from the tracheae 

 with the cuticle when the insect molts. This layer of the 

 trachea is furnished with thickenings, which 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. In some insects there are several, 

 parallel thickenings of the intima, so that, when an attempt 

 is made to uncoil the thread, a ribbon-like band is produced, 

 which is composed of several parallel threads. 



Make preparations and drawings illustrating the structure 

 of the tracheae of Corydalis. 



The Circulatory System. — Read the account of the 

 blood-vessels given in " Comstock' 1 s Manual for the Study of 

 bisects. ' ' 



Make a drawing of the heart and the wings of the heart 

 of Corydalis. Note especially the number and arrangement 



