220 CHARLES W. METZ 



clumping of chromatic materials. Good fixation with this 

 method was secured only in the case of eggs and occasional 

 large pieces of somatic tissue where* its penetrating power was 

 advantageous. 



To supplement the permanent preparations, temporary 'smears' 

 were frequently made with the use of Schneider's Aceto-carmine 

 (Stevens '08 pp. 359-360) which proved to be a valuable agent 

 for rapidly determining whether or not materials contained 

 stages suitable for study. Frequently, one gonad would be 

 prepared in this way and if found to be in the proper stage of 

 development, its mate would be fixed in Flemming. The aceto- 

 carmine preparations often gave very good figures of metaphase 

 chromosome groups, but were found to be unrehable for detailed 

 study because of the frequent distortion incident to swelling 

 or mechanical disturbance. Consequently, most of the obser- 

 vations included within this study are based upon fixed and 

 sectioned material. Sections were made 5 ju thick, except in a 

 very few cases where unusually large cells were found and a 

 greater thickness was desirable. Nearly all slides were stained 

 with Heidenhain's Iron Haematoxylin, either alone or with a 

 counter-stain of eosin or light green. Safranin was used fre- 

 quently, but gave less distinct images, and failed to differentiate 

 the finer chromatic elements as distinctly as did the haematoxylin. 



For the study of cleavage and early embryonic stages Droso- 

 phila eggs were used. These were fixed at different periods, 

 from a few minutes to a few hours, after being laid. It was 

 found necessary in most cases to puncture the eggs, in order 

 to facilitate the penetration of the fixative. When the eggs 

 were punctured, successful fixation was secured with Flemming, 

 Gilson's mercuric-nitric, Bouin, sublimate acetic and Gilson- 

 Carnoy, all of which were about equally favorable. 



A large proportion of the species included in this study have 

 been reared in the laboratory for one or more generations, and 

 the cytological material which they have furnished has largely 

 been derived from pedigree cultures. In a few instances material 

 was taken from jars of food which had been set out-of-doors, 

 but this was used only when the identification of larvae and 



