152 A. S. SHULOV AND M. P. PENER 



8 M. P. Pener and a. Shulov, Bull. Research Council Israel, 9 B (1960) 131. 



9 J. J. Matthee, Sci. Bull. Dept. Agr. S. Africa, No. 316 (1951) 1. 



10 J. C. Faure, Bull. Eutoinol. Research, 23 (1932) 293. 



11 A. Shulov and M. P. Pener, in the press. 



12 L. A. Jakhimovitch, Doklady Akad. Nauk S.S.S.R., 73 (1950) 1105. 



13 O. W. Richard and N. Waloff, Anti-Locust Bull., No. 17 (1954) 1. 



14 E. H. Slifer, J. Exptl. Zool., 138 (1958) 259. 



15 N. S. Church and R. W. Salt, Can. J. Zool., 30 (1952) 173. 



16 S. M. Zambin, Plant Protection, 19 (1939) 48. 



i'^ A. D. Lees, Cambridge Monographs in Experimental Biology, No. 4, 



Cambridge University Press, 1955. 

 1^ A. G. Hamilton, Trans. Roy. Entoniol. Soc. London, 101 (1950) 1. 



DISCUSSION 



Lees: I would like to ask Dr. Shulov whether he thinks that 

 Slifer's observation on the eggs of Melanoplus dijferentialis are 

 applicable to his species. In Melanoplus Slifer demonstrated a 

 physical barrier to the uptake of water, which is probably a 

 waxy substance removable by mild solvents, such as medicinal 

 paraffin. At the same time as the egg goes into diapause, this 

 waxy layer is deposited on the hydropyle and development 

 ceases. When the layer is dissolved and water absorbed, develop- 

 ment continues. 



Shulov: We have been unable to find a similar mechanism 

 regarding the formation of the hydropyle in Dociostaunis eggs, 

 which under our conditions have a natural diapause. We find 

 here another kind of grasshopper, Tmethys, which develops 

 without any addition of water. Its hydropyle does not show any 

 significant change during development. Therefore it appears to 

 me that the physical change around the hydropyle is generally 

 less important. 



Lees: Do you think that the low temperature acts upon the 

 embryo or upon the cells underlying the hydropyle? 



Shulov: I could not say, since we failed to isolate viable 

 embryos. 



Galun : Did you ever try to break the shell mechanically, in 

 the case where the composition of the waterproofing material is 

 unknown? 



