490 PROCEEDINGS OF THE AMERICAN ACADEMY. 



bins forficatus), :01 ; P. Bouin, :00, :01, :03, :03^ :04 ; P. et M. Bouin, 

 :02, Lithobius forficatus and Scolopendra morsitans ; P. Bouin et R. 

 Collin, :01, Geophilus linearis. 



The results obtained by these authors differ so markedly in several 

 important particulars from those obtained by myself (Blackman, :01, 

 :03, :05, :05^) on Scolopendra and by Medes (:05) on Scutigera that 

 it seemed advisable to extend the comparative study to the genera 

 upon which they had worked. What I consider the important dis- 

 crepancies between the observations upon American and those upon 

 European forms have to do with the condition of the chromatin during 

 the growth period and its later behavior in the prophase. According 

 to my observations upon the two species of Scolopendra, the chromatin 

 during the growth period is not arranged in the form of a spireme, or 

 reticulum, throughout the nucleus, but the threads are aggregated into 

 a very dense mass, the karyosphere, and at the beginning of the pro- 

 phase the chromosomes arise from this mass directly. The observa- 

 tions of Medes (:05) show that an essentially similar condition exists 

 in Scutigera. All the observations upon the European forms, however, 

 except the early ones of Carnoy ('85) upon Lithobius and Scutigera, 

 seem to lead to the conclusion that the large intra-nuclear bodies seen 

 in all chilopod spermatocytes are true nucleoli and have no genetic 

 relation to the prophase chromosomes. As will be seen later in this 

 paper, my present observations on Lithobius confirm my earlier ones 

 on Scolopendra. 



Technique. 



In the preparation of the material much difficulty was at first ex- 

 perienced in obtaining a good fixation of all the cell structures, owing 

 to the peculiar character of the cytoplasm. Thus, in the early study, 

 a large number of fixing reagents were used, including the following : 

 Flemming's strong solution, Flemming's weak solution, Gilson's fluid, 

 Perenyi's fluid, Merkel's fluid, and various picro-acetic and sublimate- 

 acetic mixtures. Of tliese, much the best results were obtained with 

 Gilson's nitric-acetic-sublimate mixture. While the results of this fixa- 

 tion were not always entirely satisfactory, the majority of preparations 

 thus obtained apparently left nothing to be desired. In later studies 

 Benin's pi eric -acetic- form ol mixture was tried, but the results were 

 much inferior to those obtained with Gilson's fluid. 



The sections were cut with the Minot rotary microtome, the thick- 

 ness varying from 2 to 6 micra, and were affixed to the slide by means 

 of very dilute albumen water. The sections were then stained by one 

 or another of a number of methods, the best cytological results being 



