EFFECTS OF LOW TEMPERATURE ON COCCID EGGS. 71 



mens and thermometer, the -empty annular chamber for the freezing 



mixture, filled through a short 1 finch 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 larvae were killed at a temperature above 32° F.. and eggs hatched 

 after being subjected to 2o° 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 larvae 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 larvae 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 eggs 

 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 

 antenn;e. 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 thai the 

 limit was reached. The eggs of Parlataria pergandii and Mytilattpi* cilri- 

 cola appeared to require a lower temperature tor destruction of their 

 vitality than the eggs of M. gloverii. Special experiments for this purpose 

 showed that there was only a delay of the changes of appearance, no 

 eggs hatching after a temperature of 24° F. To be practically service- 

 able, artificial conditions in experiments must approach sonic form o\ 

 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 



