516 PROCEEDINGS OF THE AMERICAN ACADEMY. 



"When the centrosomes are at opposite sides of the cell the nuclear 

 membrane breaks down, and its component parts become rearranged 

 to form a spindle. The linin netwoi'k is transformed directly into the 

 mantle fibres. 



The nuclear spindle remains entirely disti7ict from the centrosomes 

 and astral systems. Its fibres do not converge at a special point at 

 each pole, but end free in the cytoplasm, the poles of the spindle 

 thus being truncate. Each mantle fibre, however, points directly 

 toward the centrosome. 



The distinction between nuclear substance and cytoplasm may he 

 readily seen up to the late anaphase of the first division. 



The second division follows very closely on the first. The centro- 

 somes separate and move apart upon the cell membrane, forming a 

 spindle similar to that of the first spermatocyte. 



The first maturation mitosis results in a longitudinal or equation 

 division of the chromosomes, while the second is the reduction division. 

 Evidences of this are seen in the sequence of cleavages in the pro- 

 phase, in the attachment of the mantle fibres during the metaphase 

 of the first mitosis, in the shape of the daughter chromosomes during 

 the anaphase and telophase of the first division, and in the shape of the 

 dyads and their position in the equatorial plate of the last division. 



Laboratory of Histology and Embryology, 

 Western Reserve University, 

 Cleveland, Ohio, May 21, 1906. 



Bibliography. 



Blackman, M. W. 



: 01. The S[)eniiatogenesis of the Myrinpods. I. Notes on the Spermato- 

 cytes and Spermatids of Scolopendra. Kansas Univ. Quart., Ser. A., 

 Vol. 10, No. 2, pp. 61-76, pi. 5-7. 

 Blackman, M. "W. 



:03. The Spermatof^enesis of the Myriapods. 11. On the Chromatin in 

 the Spermatocytes of Scolopendra heros. Biol. Bull., Vol. 5, pp. 187- 

 217, 22 fi<,'. 

 Blackman, M. W. 



:05. The Spermatogenesis of the Myriapods. III. The Spermatogenesis 

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 No. 1, pp. 1-138, 9 pi. and 9 fig. 

 Blackman, M. "W. 



: 05^ The Spermatogenesis of the Myriapods. IV. On the Karyosphere 

 and Nucleolus in the Spermatocytes of Scolopendra suhspini]ies. Proc. 

 Amer. Acad. Arts and Sci., Vol. 41, No. 13, pp. 331-344, 1 pi. 



