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THE AMERICAN NATURALIST [Vol. XLIX 



6. Curious curled hairs on front legs. 



7. Marmorated thorax. 



8. Entirely black, except brownish antennae and lighter face. 

 All the species are new except two, one of these being the D. 



ampelophila of Morgan's experiments, the prior name for which 

 is D. melanogaster Meigen. One of the new species, D. similis, is 

 based on males differing from D. melanogaster in lacking the 

 large combs on the front legs, having instead only minute combs 

 which require a high magnification to be seen. In other respects 

 the flies are almost exactly as in melanogaster, and in the female 

 sex it is practically impossible to distinguish between the species. 

 There are in addition five females resembling melanogaster and 

 similis, but differing in a detail of the venation. May we not 

 suppose that D. melanogaster was introduced into the Seychelles 

 by man and that D. similis and the females (left unnamed) 

 with peculiar venation have arisen from it by mutation since 

 that time? T. D. A. Cockereel 



STEKILITY IN A SPECIES CROSS 



Professor J. A. Detlefsen, of the University of Illinois, has 

 recently published an interesting paper entitled "Genetic Stud- 

 ies on a Cavy Species Cross." 1 Several wild eavies from Brazil 

 (Cavia rufescens) were crossed with domestic guinea-pigs (C. 

 porcellus) and a study of the hybrid offspring was continued 

 for seven generations. The experiments were begun in 1903 by 

 Professor Castle who turned them over in 1909 to Professor 

 Detlefsen. They were carried on at Harvard and at the Bussey 

 Institution. The paper is divided into three parts; the first two 

 treat respectively of the genetics of color and coat factors, and 

 growth and morphological characters; the third and most im- 

 portant deals with a study of the sterility of hybrids. 



Cavia rufescens differs from the guinea-pig in several charac- 

 ters. In size it is about half as large as the guinea-pig. It has 



than tame agouti <jruiriea-pigs. owinu' to the yellow bands in the 

 ticked hair beimr much reduced. The bollv of the wild species 

 varies from a light yellow to a slightly ticked condition. In 

 agouti guinea-pigs the belly hair is usually yellow with a dark 



of the difference in size. All Fj males from such crosses were 

 i Carnegie Inst. Publication No. 205, 1914. 



