EFFECTS OF LOW TEMPERATURE ON COCCID EGGS. 71 
meus and thermometer, the empty annular chamber for the freezing 
mixture, filled through a short 1?-inch tube. 
Method of using: The specimens and registering maximum and min- 
imum thermometer were placed in the central chamber, the freezing 
mixture placed in the empty chamber, and the temperature allowed to 
gradually sink to the desired point, the indices of the thermometer then 
set to the mercury, and all closed by the heads for the desired time. 
On opening, the thermometer readings were at once taken and the tem- 
perature allowed to rise gradually to that of the atmosphere. The 
freezing mixture found to be most satisfactory was ice and salt, varied 
in proportion as required in each case. As will be seen by the table, 
the larvee were killed at a temperature above 32° F.,and eggs hatched 
after being subjected to 25° F. 
In experiments where, as in these, there is no previous experience to 
guide the examiner, it is necessary to make various experiments for in- 
struction as to the value of appearances. Sometimes larvie retain for 
several days an apparently natural appearance, leaving it doubtful 
whether their final death is the result of the temperature or want of food. 
If a small beam of the sun’s rays be brought to a focus on the stage of 
the microscope, the larve placed on a slide, the living larva on being 
brought into the focus of the rays always moves quickly, draws up its 
sucking tubes, and otherwise shows signs of life, the dead larva show- 
ing no motion under the same influence. 
The motion of the one is not attributable to heat on inert matter, but 
to sensibility indicating life, and affords a method of examination be- 
fore the question of starvation can arise. At moderate temperatures, 
30°-32° F., some eggs turn brown and collapse, whilst others, even in 
the same scale, retain their form and color. This was for a long time 
unaccountable; at length the brown was found to characterize eges 
very near hatching. In experiment No. 10, where some eggs hatched 
after a temperature of 25° F., out of a large number only three hatched, 
and of these three only one had strength sufficient to slowly leave the 
position of the eggs; the others showed life by motion of their legs and 
antenne. As a temperature of 19° F. was reported here last winter 
without clearing off the coccids, a lower temperature was supposed to 
be necessary, and the first experiments were at 16° F.; then, as results 
were ascertained, higher and higher until at 24° F. it appeared that the 
limit was reached. The eggs of Parlatoria pergandii and Mytilaspis citri- 
cola appeared to require a lower temperature for destruction of their 
vitality than the eggsof M. gloverii. Special experiments for this purpose 
showed that there was only a delay of the changes of appearance, no 
eges hatching after a temperature of 24° F. To be practically service- 
able, artificial conditions in experiments must approach some form of 
the natural condition of which information is required. In these experi- 
ments the nearest practical approach to nature was taking the insects 
at the greatest exposure in a still atmosphere. If, then, the temperature 
