BLACKMAN: SPERMATOGENESIS OF THE MYRIAPODS. 71 



lengthening of the cell. When the spermatid has reached the stage 

 shown in fig. 85, the cell outline in the region posterior to the nucleus 

 is very difficult to follow. 



An acrosome first appears at this stage, at the side of the nucleus 

 opposite the base of the axial filament. This, at this time, is a spatu- 

 late vacuole, which shows no affinity for chromatin stains. In later 

 stages this body increases much in size and stains weakly with iron- 

 haematoxylin. ( Figs. 38, 39.) 



Concerning the later changes in the spermatid I will say nothing in 

 this paper, but will merely show a few of the observed stages by draw- 

 ings. 



IV. — COMPARISON OF LITERATURE. 



The Accessory Chromosome. — Until quite recently the true nature 

 of the accessory chromosome was not understood, and by various 

 writers it has been classified among that very ill-defined group of 

 bodies, the nucleoli. It was first observed by Henking,' and by him 

 called a nucleolus. Later observers, Vora Rath,** Wilcox,'"* Moore, ^" 

 and Wagner,^^ have evidently had much the same understanding 

 of its nature, as they classified it similarly. In 1898 Montgomery^"-* 

 found the same element in the testicular cells of Pentatoma, but evi- 

 dently did not fully understand its true character, as he called it the 

 '• chromatin nucleolus." 



In 1898 McClung^'^ first correctly interpreted the character of this 

 element. He described it as a metamorphosed chromosome, and to it 

 applied the name "accessory chromosome." 



In a paper which appeared the latter part of the same year, Paul- 

 mier^* recognized its chromosomal nature and designated it the "small 

 chromosome." This name appears to have been unfortunately chosen, 

 as in many animals this element is the largest and most conspicuous 

 chromosome in the cells. In his material, Anasa tristis, the accessory 

 chromosome takes on the shape of a completely formed tetrad without 

 l)assing through any of the preceding .stages. In the first spermato- 

 cyte division it is divided along with the other chromosomes, but in 

 the second, after remaining in the equatorial plate for some time, goes 

 to one pole undivided. 



7. Henking, H., 1891: "Ueber Spermatogenese und derea Beziehung zur Eutwicklung bei 

 Pyrrhocoris apterus." Zeitsch. f. Wissensch. Zool. Bd. XXV. 



8. Vom Rath, C, 1892: "Zur Kenutniss der Spermatogenese von Gryllotalpa vulgaris." 

 Archiv f. Mikro. Anat., Bd. XI. 



8. Wilcox, E. v., 1895: " Spermatoe-onesis of Caloptenus femur-rubrum and Cicada tibi- 

 cen." Bull. Mus. Comp. Zool., vol. XXVII. 



10. Moore, J. E. S. : "On the Structural Changes in the Reproductive Cells during the Sper- 

 matogenesis of Elasmobranchs." Quart. Journ. Micr. Sci., vol. XXXVIII. 



11. Wagner, J., 1896: " Beitrage zur Kenutniss der Spermatogenese bei den Spinuen." Arb. 

 Nat. Qes., St. Petersburg, vol. XXVI. 



12. Montgomery, T. H., jr , 1898 : The Spermatogenesis of Pentatoma up to the Formation of 

 the Spermatid." Zool. Jahrb. Bd. XII. 



13. McClung, C. E., 1899, loc. cit. 



14. Paulraier, F. C, 1899, loc, cit. 



