272 CHROMATIN, ANIMAL CHROMOSOMES, NUCLEOLI 



638. Somatic Divisions. Both prophase and metaphase stages 

 should be sought in the brain or in the large ganglia of young 

 larva?. Dissections can be made in Ringer's solution (cold- 

 blood formula) or in 0-73 per cent, salt solution. Navaschin's fluid 

 has been widely used as a fixative for such tissue, and sections 

 should be stained in iron ha-matoxylin or in Newton's iodine 

 gentian violet. According to the recent work of Prokofieva 

 {Zeitsch. Zellforsch. mikr. Anat., xxii, 1935, p. 254) the chromo- 

 formol fixatives of Levitsky (§ 1330) are valuable for showing the 

 constrictions. The morphology of the X chromosome shows 

 best after treatment with equal parts of 10 per cent, formol and 

 1 per cent, chromic acid. For the autosomes she uses 6 parts 

 of 50 per cent, formol and 4 parts of 5 per cent, chromic acid. 



639. Drosophila Eggs and Embryos. The first step is to 

 remove the chorion from the freshly laid eggs. This is easily 

 done in the following way : Several years ago Professor J. T. 

 Patterson, at the University of Texas, found that if a little quick- 

 drying glue is smeared on a slide and the eggs are placed on this 

 fresh surface, when the glue is dry the chorion may be removed 

 from the eggs by pressing against one side with a blunt needle. 

 The de-chorionated eggs are next punctured on the convex 

 side, slightly posterior to the middle with a very sharp needle. 

 HuETTNER {Jour. Movph., xxxvii, 1922, p. 385) found that 

 Kahle's formol-alcohol-acetic fixative gave the best results. 

 Others prefer Petrunkevitch's fluid. Very young ovarian eggs 

 are well preserved with Flemming's solution, as described above, 

 and section easily. 



640. Salivary Gland Chromosomes. The general experience has 

 been that old fat larvae, raised on rich yeast food at a low tempera- 

 ture (from 16° to 20° C), show the largest chromosomes and give 

 the best preparations. The glands are dissected out in Ringer's 

 solution (cold-blood formula) or in a 0-73 per cent, salt solution. 

 Subsequent treatment depends on the type of preparation desired. 



For a study of the living chromosomes the glands may be 

 mounted on a clean slide with some of the dissecting medium 

 and the coverslip sealed with vaseline. Care should be taken to 

 prevent evaporation during the process. Perhaps it would be 

 better to adapt the method recently used for the study of Chiro- 

 no7nus chromosomes by Bauer {Zeitsch. f. Zellforsch. u. mikr. 

 Anat., xxxiii, 1935). Bauer dissects large larvae in their own body 

 fluids and with a pipette transfers the glands, along with some 

 of the ha?molymph, to a clean slide, where several large drops of 

 paraflin oil are added. A coverslip is now placed over the whole 

 mass and the preparation is ready for study. It will remain fresh 

 up to twenty-four hours. 



641. For temporary aceto-carmine preparations. Painter 

 {Genetics, xix, 1934, p. 175) uses the following method : After 



