REPORT OP THE ENTOMOLOGIST. 227 



•WINTEEING THE EGGS. 



The egg of the silk- worm moth is of a bright yellow color when laid, 

 but, if properly fecundated, it turns gradually, in five or six days, to an 

 ashen or bluish gray, or sometimes to an earthy yellow. If sterile it 

 retains its original hue. It is oval and slightly flattened in shape, beiug 

 indented on one side. Near one end a small spot may be observed. 

 This is called the micropyle, and is the opening through which the fecun- 

 (latiug liquid is injected just before the egg is deposited by the female. 

 After fecundation and before deposition the egg is covered with a 

 .liiiiuniy varnish which closes the micropyle and serves also to stick to 

 the object upon which it is laid. It is at the micropyle also that the 

 young larva always eats its way through the shell. The mean diameter 

 of the egg is about 1 millimeter (one twenty-fifth of an inch) though it 

 varies with the race. In a standard ounce of 25 grams (28^ grams 

 = 1 oz. avoirdupois) there are about 50,000 eggs of the small Japanese 

 races, 37,500 of the ordinary yellow annual varieties, and from 30,000 

 to 35,000 in the races with large cocoons. The specific gravity of the 

 eggs is slightly greater than water, Haberlandt having j)laced it at 1.08. 



The eggs may be removed from the cloths on which they are laid by 

 soaking them some time in water, which softens the varnish surrounding 

 them, and tlien scraping them off with a paper-cutter or an ordinary 

 table-knife. 



While changing color the contents of the egg undergo a chemical 

 change, absorbing oxygen and giving off carbonic acid. This absorption 

 of oxygen is very active during the first six days, after which it rapidly 

 declines and continues at a very low figure during the months which 

 precede the hatching. The eggs should, therefore, bo wintered in such 

 a manner that they may have plenty of air ; otherwise their develoi^ment 

 will bo seriously interfered with. They must not be packed in too thick 

 layers, but should be spread out thinly. For these reasons the eggs at 

 this Department are kept through the winter in boxes of perforated tin, 

 the bottoms of which have a surface of 6^ square inches, each box con- 

 taining not more than one-quarter of an ounce of eggs. 



The atmosphere in which the eggs are kept should neither be too dry 

 nor too humid. M. Beauvais found a saturation of 50 per cent, to be the 

 most suitable condition of the air, as when it is below that point the 

 liquids of the egg evaporate so rapidly as to require a highly saturated 

 atmosphere for their incubation. Excessive moisture, on the other hand, 

 will assist the formation of mold, which will quickly injure the contents 

 of the egg. The eggs should be frequently inspected, and whenever 

 such mold is discovered it should be quickly brushed off and the eggs 

 removed to a drier locality. 



Under natural conditions the egg undergoes a partial development as 

 soon as laid, as shown by its changing color. After oviposition, imd 

 until subjected to cold, the eggs of the annual races are not capable of 

 hatching out. This is the rule, although we often find in a batch of an- 

 nual eggs a few accidental bivoltins that hatch some fifteen days after 

 they are laid. The number, however, is very slight, and it has been de- 

 termined that the temperature to which they are submitted in no way 

 alters the result. During this period, which we will call prehibernal, 

 tlie eggs may be kept at any ordinary temperature, hpwever warm, but 

 once they are submitted to the cold of winter a certain change takes 

 place in them, the nature of which has not as yet been determiued, and 

 their subsequent warming may then result in hatching. As in our 

 climate warm days are quite frequent in late winter, it becomes of the 



