280 APPENDIX. 



quite extinct, while the latter lose their abundance. Hence, to the 

 annual migrations must be added others marked by cycles of years; 

 and not necessarily in lines of longitude, but as frequently in those 

 of latitude. 



Birds come and go ; but whence they come and whither they go 

 is a matter of conjecture. One morning the trees of Independence 

 Square, in the heart of Philadelphia, were found filled with crows. 

 Not a caw was to be heard nor a movement seen. The birds 

 appeared to be awaiting in silence further instruction. After some 

 time several new-comers glided among them, threading their way 

 through all the flock, when suddenly the teeming thousands rose 

 simultaneously and departed as mysteriously as they came. 



Glacier Theory. A recently proposed explanation of the annual 

 migration of birds is called the "glacial," and is receiving much 

 attention from ornithologists. It implies that in the so-called "Gla- 

 cial Period," species now incubating near the present southern limit 

 of perpetual frost, followed the retreat of the ice northward in suc- 

 cessive periods, but returning each fall through the influence of 

 habit to their original habitat successive ages increasing the length 

 of their migration. This theory also presents difficulties, and the 

 problem may be, considered as yet unsolved. 



HINTS FOR PRESERVING SKINS OF MAMMALS 



AND BIRDS. 



Mammals. Stuff cotton into the mouth, nostrils, large shot-holes, 

 etc. Split the skin from the top of the breast-bone to the tail, being 

 careful not to cut through the abdominal muscles. Push off the 

 skin, not pull it off from the body. Separate the limbs from the 

 body, preserving all the bones, including the shoulder-blades. With 

 a cleft stick slide out the tail, if covered with hair ; but, if naked 

 like the tail of a rat, cut it off, as it can not be skinned. Turn out 

 the legs and clean away all flesh to the toes, leaving the tendons 

 around the joints. Skin over the head, taking off the ears close to 

 the skull, and preserving uninjured the eyelids and lips. Cut into the 

 mouth on the inside of the teeth only to remove the tongue. Cut 

 off the head, cleaning away all muscle and taking out the brain and 

 eyes. While the skin is wrong side out and moist, sprinkle it 

 thoroughly with a mixture of equal parts, by weight, of powdered 

 alum and arsenic. Fill the eye-orbits with cotton. Push the skull 

 and legs back, supplying the place of the flesh in those portions with 



