298 PROCEEDINGS OF THE ACADEMY OF [April. 



number) one shows marked individuality throughout ; it is always in 

 close connection with the plasmasome, stains deeply when the other 

 chromosomes have lost their staining properties, and in early prophase 

 is seen to take a form similar to the other chromosomes. Dederer, like 

 Stevens, interprets this chromosome, as a pair of equal idiochromosomes 

 of the Nezara type. 



II. Material and Methods. 



My material was largely collected in the vicinity of Philadelphia, and 

 was fixed at intervals throughout the pupal stage. The ventral wall of 

 the abdomen was cut along its length and pinned back ; after removing 

 the intestines, the fixing fluid was immediately injected into the body 

 so that the testes were fixed during dissection. Of a number of solutions 

 used, Flemming's strong solution, Hermann's platino-aceto osmic, and 

 Gilson's mercuro-nitric gave the best results. Material fixed in Flemming 

 for from six to twelve hour-, washed the same length of time in run- 

 ning water, and preserved in various percentages of alcohol, was most 

 satisfactory: here both chromatic and achromatic structures were 

 sharply defined, and the shrinkage which a longer fixation so often 

 produces was avoided. Preparations which had been so fixed and run 

 through the alcohols were then cleared in xylol and embedded in hard 

 paraffin with a melting point of 55° C. Sections were cut from three to 

 nine microns thick. Various stains were used: The best cytological 

 results were obtained with Heidenhain's hematoxylin followed by 

 orange-G; this stain gave an almost perfect definition and was used for 

 all general and for most of the detailed work. Thionin . I )elafield's haema- 

 toxylin, safranin and light green, Hermann's saf ran in-gentian-violet, 

 Auerbach's and Biondi-Erlich's stains were used for micro-chemical 

 tests, but with at best indifferent success. The greatest difficulty 

 encountered in technique has been in finding a stain which will clearly 

 differentiate basichromatin from oxychromatin. In the early spring 

 of 1907 I began to make smear preparations by spreading bits of testes 

 upon a slide with dissecting needles, and after drying, staining them in 

 Bismarck Brown for twenty-four hours as described by Foot-Strobell 

 (1905). These proved very helpful. The cells stretched in drying and 

 were several times larger than those in sections, so that they were espe- 

 cially useful in studying spireme stages and in counting chromosomes 

 in cell plates. Their disadvantage lies chiefly in the lack of the sequence 

 of stages so clear in sections, but when studied in connection with sec- 

 tions and particularly when the number of chromosomes is small, they 

 have been invaluable. 



