370 SECTIONAL TRANSACTIONS.— D. 



sequence of desert rainfall. No correlation is found between European 

 outbreaks and the rainfall of those North African meteorological stations 

 for which records are available, but this may be due to the paucity of suitable 

 figures. 



Records are available for Europe over a period of one hundred and 

 thirteen years, and for America for sixty years. A tendency is found for 

 both years of unusual abundance and years of scarcity to occur simultane- 

 ously in Europe and America, showing that the cause of the outbreaks 

 must be sought in some factor common to the two continents. There seems 

 to be some correlation between outbreaks and the sunspot cycle, but the 

 figures are barely significant. The outbreaks tend to occur away from the 

 sunspot minima. , 



Mr. A. Roebuck. — The chafers of Nottingham and Lincolnshire (3.15). 



Tuesday, September 7. 



Dr. Flora E. Cochrane. — The activity of genes in development (lo.o). 



Work on the development of eye pigment in Drosophila has shown that 

 pigment normally appears in the eyes at two distinct though consecutive 

 times during pupal life. Eye-colour mutant genes affect either or both of 

 these phases of development but allow the remainder of the development 

 to proceed as in wild type. Histological studies have shown that eye-colour 

 is due to the presence of pigment granules in definite pigment cells of which 

 there are two kinds. Genes which affect eye-colour do so by altering the 

 distribution of these granules, usually by suppressing their formation or by 

 retarding their development ; no gene acts to increase the number of granules 

 beyond the number present in wild type. All genes so far recorded, with 

 one exception, have a quantitative effect, the effect in the exceptional case 

 being qualitative. 



Studies of the testes of wild type and various mutants of Drosophila 

 pseudo-obscura have shown that their colour appears and develops at the 

 same time as the late phase eye pigment appears. It has also been shown 

 that the genes which affect the eye pigment laid down during the late phase 

 of development affect the testis colour in the same way and to the same extent 

 while genes which affect the early phase of eye pigment development only, 

 have no effect upon testis colour. 



Mr. H. D. Slack. — Chromosome behaviour and taxonomic groups (10.30). 



The value of chromosome behaviour as a means of providing further data 

 for the demonstration of taxonomic relationships in animal groups has been 

 recognised by many investigators. This comparative study deals principally 

 with a single sub-order of insects, the Hemiptera-Heteroptera. About forty 

 species were collected from one district, the country surrounding the city 

 of Edinburgh. These are distributed among five families representing the 

 two primary divisions, Gymnocerata and Cryptocerata. Studies of equiva- 

 lent stages of chromosome behaviour in the development of the male germ 

 cells are used to compare cytological grouping with phenotypic characters 

 on which the taxonomic relationships are based. The systematic positions of 

 the species represented are such as to allow comparison between the two 

 primary groups, between families within these groups, and between smaller 

 units within the families. By this treatment substantiation or insubstantia- 

 tion of relationships implied by structural similarities is demonstrated and 



