940 RECORD OF CURRENT RESEARCHES RELATING TO 



cocoon preserves the chrysalis from extreme cold by finding in the 

 month of March (1872) some cocoons of Attacus cynthia suspended to 

 the branches of the trees in the abbey garden of 8aint-Germain-des- 

 Pres, Specimens of these moths had been introduced by Babinet in 

 1860, and, unattended by any one, had bred there since; the 

 successive generations successfully supporting the cold of eleven 

 winters. The winter of 1871-2 had been excessively severe. In 

 Paris the mean temperature from the 8th to the 19th December, 1871, 

 had remained at — 9° C. and on the 21st the thermometer descended 

 to — 20°, remaining at — 18° for twenty-four hours. Dr. Bellesme 

 was therefore surprised to find the chrysalids in a complete state 

 of preservation, the perfect insect emerging in due course. This 

 unlocked for resistance to congelation could only be due to one 

 of two causes ; either the almost absolute non-conductivity of the 

 silky covering, or the production of a notable quantity of heat on the 

 part of the insect. The latter alternative seemed improbable con- 

 sidering the immobility of the nymph. 



Dr. Bellesme proceeded to test the conductibility of the cocoon, and 

 having opened one and extracted the chrysalis, he inserted the bulb of a 

 sensitive thermometer in its place, securing the cocoon round it with an 

 elastic band, and arranged it so that the bulb of the instrument did not 

 touch the cocoon anywhere. The cocoon thus prepared was intro- 

 duced, in company with a thermometer for comparison, into a testing- 

 glass, surrounded by a freezing mixture. Before the experiment both 

 thermometers marked 18° ; five minutes after their introduction into 

 the test-glass they were withdrawn, when both marked 9°. On 

 suspending them in the oj)en air the comparison thermometer rapidly 

 rose, and in a few moments had regained its former level of 18° ; 

 after ten minutes, the thermometer which had the cocoon tied over it 

 stood at the same point. 



If, therefore, the nymph resists congelation, it does so by virtue 

 of a continuous and considerable disengagement of heat. It is 

 extremely probable that this heat is produced at the expense of the 

 organic transformations which take place within. There is the dis- 

 appearance of certain muscles which have served the larva and the 

 formation of new ones to be used by the perfect insect. But the muscu- 

 lar system of the larva is far more considerable than that of the 

 perfect insect ; all the heat rendered available by the destruction 

 of the old muscles is not, therefore, used up in the construction of 

 new ones. Moreover, uric acid and its derivatives are very abun- 

 dant in the recently metamorphosed insect, another sign of the 

 existence of active combustion during the nymphal period. To 

 these organic-chemical phenomena must then, apparently, be attri- 

 buted the facility with whicli insects, in course of transformation, 

 support prolonged low temperatures. 



Wing-muscles of Insects.* — N. Poletaiew describes the difference 



between the wing-muscles of the Lepidoptera and of the Libellulidse. 



Those of the former may be arranged in three groups : (1) a median 



* 'Zool. Anzeig.,' iii. (1880) p. 212. 



