434 SUMMARY OF CURRENT RESEARCHES RELATING TO 



dissecting and packing into the pouch. But with some objects such as 

 small eggs, etc., not injured by exposure to the dissecting fluid, packing 

 may be done before fixation. 



Once a packet is made and the membrane has hardened in the 

 fixative or alcohol it may be handled readily without fear of losing 

 the contents. Reagents, including paraffin, penetrate the membrane 

 readily, so that dehydration and embedding may be done rapidly. It 

 is easy to secure species of Drosophila of various sizes around garbage, 

 decaying fruit, etc., and so obtain pupa-skins of sizes adai)table to 

 individual needs. By putting a few flies in a cotton-j^lugged bottle 

 with ripe banana (or something similar) and a httle paper, practically 

 any desired number of pupai may soon be obtained. 



A supply of pupa-skins sufficient for months or years may be made 

 up at one time and kept in 30 p.c. or 50 p.c. alcohol until needed. 



This method may seem tedious, but with practice it proves rapid 

 and efficient, and ensures — 



1. Standardization of size of packets. 



2. Convenience of size of packets. 



3. Minimum amount of enclosing tissue together with close aggre- 

 gation of objects themselves, making it unnecessary to section a packet 

 much larger than the mass of objects themselves. 



4. Transparency of the enclosing membrane at all stages, permitting 

 orientation or examination of the contents. 



5. Cleanliness of membrane and freedom from dirt and grit such 

 as is often encountered in amphibian epidermis. 



6. Relative freedom from extraneous tissue or material in the 

 sections. 



