STUDIES ON THE GERM CELLS OF APHIDS. 



By N. M. Stevens. 



INTRODUCTION. 



My previous report on the germ cells of aphids was based on a 

 study of the parthenogenetic and winter eggs of Aphis rosae, the 

 brown rose aphid, and of the spermatogenesis of Aphis oenotherae, 

 found on the inflorescence of Oenothera biennis. 



During the past summer and autumn material from more than 

 twenty species has been collected and examined. In some cases it 

 has been possible to study all of the forms of one species, in other 

 cases only the parthenogenetic eggs, only the winter eggs, or only 

 the spermatogenesis. 



It has become evident in the course of the work that little depen- 

 dence is to be placed on the present classification of aphids, and that 

 a reclassification based on the cytology of the germ cells may be nec- 

 essary. For example, it appears that at least three distinct species 

 are usually included under the name Aphis rosae. No attempt will, 

 therefore, be made in this paper to give the L,atin names of the species 

 studied, but they will be designated by the names of their host plants, 

 and identified by brief description where it seems necessary. 



This comparative study was undertaken in the hope of throwing 

 more light on the q uestion of sex determination, and the descriptive 

 part of the paper will be followed by a further discussion of the bear- 

 ing of the facts recorded on that problem. 



METHODS. 

 The methods used were for the most part the same as in the pre- 

 vious work — fixation with Gilson's "acetic alcohol with sublimate" 

 (L,ee, sixth edition, p. 65) and staining by Heidenhain's iron-haema- 

 toxylin method. Some material was fixed in Flemming's fluid, 

 Hermann's platino aceto-osmic, and Gilson's mercuro-nitric, but such 

 fixation brought out no new points in structure, and was, in general, 

 less satisfactory than fixation with Gilson's acetic alcohol-sublimate 

 formula. The latter fluid was used at first on account of its great 



