The Zoologist— June, 1868. 1235 



one hundred and ten empty shells weigh one grain : about six thousand 

 worms are equivalent in weight to one ounce. 



I will now proceed to give some instructions as to the rearing of the 

 worm : they will be easily understood, if I have been clear enough in 

 explaining the natural history of the Polyphemus silk-worm. 



Selection and Preservation of Cocoons intended for Stock. — The 

 cocoons intended for the propagation of the species for the following 

 year should be carefully selected. As a general rule, the female larva 

 is larger than the male ; so the cocoon of a female is also larger than 

 the male cocoon. 1 estimate a cocoon to be a very good one, and the 

 pupa within healthy, when it is heavy for its size, and resists well the 

 pressure betweeu the fingers, not being deformed by it. About one 

 half of the number intended for propagation should be selected from 

 among the largest; very probably the majority will be females: the 

 other half should be selected, not among the largest nor the smallest, 

 but among the intermediate ones. When properly selected they should 

 be placed beyond the reach of rats or mice, in boxes, baskets or bags : 

 the boxes should be stored in a cold dry room or cellar, where the 

 temperature does not get above forty-five degrees, for if the tempera- 

 ture be higher they will be liable to hatch before winter. While the 

 temperature should not go above forty-five degrees, it can descend 

 indefinitely without injury to the pupa. 



Hatching out of the Moth. — Towards the end of May, in the lati- 

 tude of Boston, the temperature sometimes reaches seventy degrees. 

 I have said above that a heat of fifty or fifty-five degrees, continued 

 for some time, is sufficient to put in activity the causes which transform 

 the pupa to perfect insects. So, about the middle of May, the cocoons 

 should be taken out of the cellar and put into the hatching-room, as 

 the time approaches when the perfect insect will appear out of its 

 prison. Tables or shelves should be placed in the hatching-room to 

 lay the cocoons upon : they should be spread out, and not piled one 

 upon the other, as the insect in coming out would get to the surface 

 with difficulty : over the tables or shelves where the cocoons are 

 placed should be hung pieces of cloth, or net, to which the insect can 

 easily attach its hooks for the purpose of allowing its wings to develope. 

 The perfect insect rarely comes out before noon, and very few after 

 five o'clock in the afternoon. One should watch the .process of ex- 

 clusion, in order to help the insects when they do not readily find the 

 net, or cloth, to cling to, and also to remove those which disturb 

 others whose wings are already expanding. The rays of the sun 



