46 ARTHUR W. GREELY. 



as the Protozoa, a lowering of the temperature brings about a 

 reversal of the vital phenomena and the formation of simple rest- 

 ing stages. 



II. THE EFFECT OF VARIATIONS IN THE TEMPERATURE UPON 

 DEVELOPMENTAL PROCESSES. 



It has been frequently observed that eggs, spores, cysts, or 

 other resting stages of the motile organism which are formed to 

 tide over some unfavorable conditions in the life-history of the 

 animal, will not develop into the motile form unless they are ex- 

 posed to the very conditions that brought about their formation, 

 and normally intervene before development commences. Thus 

 Braem l found that the statoblasts of Bryozoa, and the winter 

 eggs of Apus would develop only after they had been exposed 

 to a certain degree of low temperature. In this case the phys- 

 ical change produced in the protoplasm of the egg or statoblast 

 by the low temperature seems to be necessary before the devel- 

 opmental processes can originate. 



Dr. Loeb suggested to me the possibility that the same thing 

 might be true for the development and metamorphosis of the 

 chrysalids of a common moth, Cecropia, that are formed in the 

 Autumn, but do not complete the metamorphosis until the follow- 

 ing Spring. To test this hypothesis and see if other means be- 

 sides that of low temperature would suffice to start development, 

 the following series of experiments was performed : 



On October 15, 1901, before they had been exposed to any 

 frosts, a large number of cocoons were brought into the labora- 

 tory. Many of these chrysalids were found to be parasitized by 

 an ichneumon fly, and only a small number were available for 

 the experiments. The cocoons were kept in the laboratory at 

 a temperature of 20 C. until November 27. They were then 

 divided into two lots. One lot was kept constantly at a tempera- 

 ture of 20 C., as a control series, and the other was placed out- 

 doors for six days, at a time when the temperature fell below o 

 C. each night. At the end of the six days, these cocoons were 

 brought back into the laboratory, and kept with the others at a 

 temperature of 20 C. On January 27, the chrysalids that had 



1 Braem, Jahrber, Settles. Ges. f. nat. Cult. (7,ool. Bot. Sec.), 1895, p. 2. 



