HATCHING SILKWORM EGGS. 



15 



From the fourth day on, gradually increase the temperature two 

 degrees in twenty-four hours until 73'^ F. is reached, when, at this 

 uniform temperature, hatchings will occur in ten days on an average. 

 This period, however, varies from eight to fifteen days, according to 

 race, the cold supported during the winter, the first grade of heat, and 

 the highest during the incubation, and the number of days taken to 

 pass through these two grades of heat; and also according to the 

 humidity. To obtain a good and complete hatching, a slight humidity 

 is necessary, especially during the last four or live days. To secure 

 this keep an open vessel of water near 

 the fire, or sprinkle the floor with water 

 occasionally. 



The temperature may be raised during 

 the hatching to TS'-* F. , but sudden changes 

 of heat must be avoided, and, unless the 

 newborn worms can be kept in the same 

 temperature, it is dangerous to have the 

 maximum temperature of the incubator 

 so high. 



It is better for the period of incubation 

 to be protracted than suddenly short- 

 ened. Holding the eggs at a certain tem- 

 perature, or slowly lowering the temper- 

 ature a little does no harm. When the 

 season is not propitious, the hatching 

 may in this way be retarded. 



An incubating room is preferable, be- 

 cause it also serves for the first two stages 

 of the worms, l)ut in small rearings an 

 incubator is more economical, both with regard to service and to fuel. 



For a large quantity of eggs (.5 to 10 ounces) a small incubator, 

 which is very much used in chemical lalioratories to dry substances, is 

 recommended. Any ordinar}-^ tinsmith can mak(» it. It consists of a 

 double case, cubical in form, with a zinc bottom. The space l)etAveen 

 the outer and inner walls is filled with water. The front face of 

 the cube is furnished with a glass, so that the temperature within, 

 indicated by the thermometer hanging on the glass, may be seen with- 

 out the necessity of opening the incubator. There are two openings 

 below on opposite sides to allow the cold air to come in, and an opening 

 in the center of the top to permit the outward flow of the heated air. 

 Having filled the space l^etween the walls with water, the incubator is 

 placed on a support and heated by means of a gas or oil lamp to the 

 desired degree, and, by raising or lowering the flame, a constant or 

 progressive temperature can be maintained (fig. 7). A self -regulating 



Fig. 7. — Hot water incubator. (Redrawn 

 from Verson and Quajat.) 



