Larvae and Pupae 75 



enveloping membrane of the single ova is struct- 

 urally very different from that of the massed eggs, 

 being much more elaborate. Also, as pointed out 

 by Mr. Coquillett {Science, Feb. 23, 1906), all single- 

 egg layers have toothed claws in the adult form 

 so far as known, with the exception of the genus 

 Grabhamia, while, except in this genus, all mosqui- 

 toes having simple claws form rafts. 



Resistance of Larvae to Cold. — Although so 

 marvellously delicate in appearance some of the 

 larvae are apparently able to resist much steady 

 cold, alternating low and high temperatures being 

 fatal. Some species hibernate in the larval stage. 

 O. canadensis escapes actual freezing, it is said, by 

 burrowing into the mud if he happens to hatch dur- 

 ing a thaw, and becomes nipped by the cold later on. 

 W. smithii, however, which lives in the leaves of the 

 pitcher-plants, can, as observed by Mr. Brakeley, be 

 frozen up solidly in the ice without coming to harm, 

 and melts out as good as ever. M. melanurus also 

 lives through the winter as a half grown larva, prob- 

 ably hiding in the leaves and mud. Dr. M. J. Wright 

 {British Medical Journal, io,oi,pp. 882-883) reports 

 that he saw active Culex larvae in a pool covered 

 with a thin layer of ice. One of the larvae, upon 

 coming to the surface to breathe, was frozen stiff, 

 but on being removed to a warmer atmosphere it 

 revived and was soon wriggling merrily. Then the 

 Doctor began experimenting. He placed some 

 Culex and Anopheles larvae in a cup of water. Then 

 he gradually froze the water by putting the cup in a 

 mixture of ice and salt. The wrigglers remained 



