40 SUMMARY OF CURRENT RKSEA.RCHES RELATING TO 



Inherited Linkage Variations in Second Chromosome of Droso- 

 phila. — A. H. Sturtevant(P«&/*c«^ww 278, Carnegie Inst. Washinriton, 

 lOl'.t, 307-4:1). In a female of Drosopliila mehinogaster (jtmpeJophUa) 

 that came from a stock collected in Xova Scotia, the author found two 

 genes that influence the amount of crossing-over in the second chromo- 

 some. Crossing-over, it mtij be recalled, is the interchange of blocks of 

 genes between two homologous chromosomes lying apposed. Each of 

 the genes in question, in females heterozygous for it, decreases the 

 amount of crossing-over in the region in which it lies. The author 

 indicates where the genes have their locus in the chromosome. Neither 

 of these two genes causes any change in the usual condition of no 

 iTossing-over in males. J. A. T. 



Modifying- Genes. — T. H. Morgan {Publication 278, Carnegie Inst. 

 Washing/on, 191ii, 345-88, 1 pi., 15 figs.). Notch wing is a dominant 

 character in some females of Drosopliila melanogaster, and is caused by 

 a domijiant gene in the sex chromosome. In addition to its dominance, 

 the gene produces a recessive lethal effect, killing every male that carries 

 the gene. Xotch females are heterozygous for the Notch gene. i.e. one 

 X chromosome carries the gene for Notch, the other X chromosome 

 carries its normal allelomorph. The latter saves the female from the 

 lethal effect of the Notch gene. It has been shown by Morgan that 

 mass selection on this character, carried out for twenty-four generations, 

 results in a change in the character in the direction of the selection. 

 It is also shown ingeniously that the changes brought about by the 

 selection are due to the presence in the stock of a recessive modifying 

 factor in the second chromosome. Notch females homozygous for this 

 factor give the "selected group." Those heterozygous for it, or lacking 

 it altogether, give the atavistic or original group. J. A. T. 



Minute Structure of Diptera. — P. E. Keuchenius (//'//'''• ^'eder- 

 Jand. Dierlc. Ver., 1917, 16, 1-52, 3 pis.). ' Description of the minute 

 structure of the reproductive organs, Malpighian vessels, fatty tissue, 

 epidermis and muscle in Tipida oleracea, Enxtalis tenax, E. arbi/storum, 

 Beris claripes, Lucilia csesar, and Chironomvx annularis {?). The ova- 

 rioles consist of terminal filaments, terminal chamber, and follicles, or of 

 terminal chamber and follicles, or of follicles only. In the cells of the 

 youngest follicles of IJeris and Lucilia there is merely indifferent nucleo- 

 plasm which may form the nuclei of ova or may be absorbed by the 

 growing ova without ever forming a true nucleus. An account is given 

 of the three spermothecaj, the receptacula, the seminal canal, the uterus^ 

 the vagina, and the occasional accessory glands. The Malpighian 

 tubules show a secreting synctium without cell walls. The fatty tissue 

 is heterogeneous, even in the same animal. There is sometimes {Eristalis). 

 an intimate contact between liparocytes and oenocytes. The epidermis 

 is usually very delicate and its nuclei are often difficult to find ; in 

 Beris it is structureless ; in Cldrononius it is well developed. In Erislalis 

 arbustorum the muscles show not only a terminal insertion, but also 

 a lateral attachment to the epidermis. Different forms of striped muscle 

 are described. • J. A. T. 



