48 



With a hypodermic syringe inject into the body-cavity of a living larva a 

 solution of lampblack or of carmine.* After about an hour, drop the larva 

 into boiling water and leave it there till killed, which will require from ten 

 to twenty seconds ; then transfer it to cold water. In specimens prepared 

 in this way the heart will be found fVUed with coagulated blood, which is 

 rendered more easily seen by the presence in it of the lampblack or carmine. 

 The relation of the valves to the segments of the body can be best deter- 

 mined in specimens from which the dorsal body-wall has been removed 

 from over the heart, the specimens being studied from the dorsal aspect. 



In Corydalis the heart contains eight sets of valves, and the aorta two. 



Make figures showing the position and form of the valves of the heart 

 and of the aorta. 



The pericardial diaphragm or the " wings of the 

 heart." — Take the specimen which was prepared so as to 

 show the heart and the aorta. Empty the water from the 

 dish, containing the specimen, and place a few drops of 

 haematoxylin on it ; after one or two minutes wash off the 

 stain, and cover the specimen with clear water. Careful 

 examination will now reveal the dorsal diaphragm, which is 

 so delicate that it is seen with difficulty unless stained. 



This diaphragm is attached along its middle line to the 

 ventral surface of the heart. Each lateral edge of the 

 diaphragm is attached to the body-wall in sixteen places, 

 along two lines. 



Represent the pericardial diaphragm upon the drawing of 

 the heart and aorta already prepared. 



There are differences of opinion as to the function of the 

 pericardial diaphragm. f It seems to us that an important 

 function, if not its chief function, is to protect the heart 

 from the peristaltic movements of the alimentary canal. It 

 also supports the heart ; and may play a part in its expan- 

 sion. 



*.2 g. lampblack, .2 g. gum arable, 15 c. c. water; or .4 g. carmine, .2 g. 

 gum arabic, 15 c. c. water. 



t See Packard. Text Book of Entomology, pp. 401, 402. 



