Proceedings of the American Academy of Arts and Sciences. VOL. XLII. No. 19.- FEBRUARY, 1907. CONTRIBUTIONS FROM THE BERMUDA BIOLOGICAL STATION THE SPERMATOGENESIS OF THE MYRIAPODS. V. ON THE SPERMATOCYTES OF LITHOBIUS. BY MAULSBY W. BLACKMAN. WITH TWO PLATES. THE SPERMATOGENESIS OF THE MYRIAPODS. V. ON THE SPERMATOCYTES OF LITHOBIUS.1 BY MAULSBY W. BLACKMAN. Presented by E. L. Mark, December 12, 1906. Received November 22, 1906. FOR a number of years the author has been collecting material for a comparative study of the spermatogenesis of the principal groups of the Chilopoda. Five papers based upon this material have already been published; a series of four papers (Blackman, :01, :03, :05, :05") upon two species of Scolopendra (S. heros and S. subspinipes) and one paper upon Scutigera forceps by Medes (:05). In the present article it is my purpose to carry this comparative study further. The present paper is based upon a study of the spermatocytes in three species of the genus Lithobius and is from material collected in three widely separated localities. The principal observations were made on the testes of Lithobius mordax, collected in the vicinity of Lawrence, Kansas, during the spring and summer of 1902 and 1903. Using as a basis the knowledge gained from the study of this species, additional observations have been made upon Lithobius sp. and Lithobius multidentatus, with a view to comparison. The material of Lithobius sp. was collected by the author near Flatts, Bermuda, during July, 1903, while working at the Bermuda Biological Station for Research; that of Lithobius multidentatus was collected near Cambridge, Mass., during October, 1904. At the time this comparative study of myriapod spermatogenesis was begun, no detailed work upon the germ cells of chilopods had been attempted under modern conditions of technique. The only observations upon this material then published were those of Carnoy ('85) in his classical Cytodierèse chez les arthropodes, and those of Prenant ('87, '92). Since then, however, a number of papers based upon the sperm cells of myriapods have appeared. Of those dealing with problems touched upon in this article the chief are those by Meves and von Korff (Litho 1 Contributions from the Bermuda Biological Station for Research, No. 10; and from the Laboratory of Histology and Embryology, Western Reserve University. bius 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 discrepancies 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 prophase the chromosomes arise from this mass directly. The observations 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 experienced 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 sublimateacetic mixtures. Of these, much the best results were obtained with Gilson's nitric-acetic-sublimate mixture. While the results of this fixation were not always entirely satisfactory, the majority of preparations thus obtained apparently left nothing to be desired. In later studies Bouin's picric-acetic-formol 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 thickness 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 |