15 



is necessary, especially during the last four or five 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 75° 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 sud- 

 denly shortened. Holding the eggs at a certain temperature, or slowly 

 lowering the temperature a little does no harm. When the season is 

 not propitious, the hatching may in this way be retarded. 



An incubating room is preferable, because it also serves for the first 

 two stages of the worms, but 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 laboratories to dry 

 substances, is recommended. Any ordi- 

 nary tinsmith can make it. It consists 

 of a double case, cubical in form, with a 

 zinc bottom. The space between 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 thermometei 

 hanging on the glass, may be seen with- 

 out the necessity of opening the incu- 

 bator. 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 between the walls with water 

 through the pipe, 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. 8). A self-regulating incubator, such as is used to 

 hatch chickens, would be more convenient, but would cost more. 



The whitening of the eggs denotes the near approach of the hatch- 

 ing. Double pieces of tulle or sheets of perforated paper sprinkled 

 over with finely cut-up white mulberry leaves should then be lightly 

 placed over the eggs to allow the outward passage of the worms as 

 soon as hatched. The object in employing two pieces of tulle or 

 paper is to prevent the unhatched eggs which cling to the sheet from 

 being removed with the newborn worms. This process must be 



165 



PiQ. 8.— Hotwaterincubator. (Redrawn 

 from Verson and Quajat. ) 



