No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 45 



IV. Spindles and Spindle Fibers. 



General Remarks. 



The various fibers and rays which form during mitosis may- 

 be conveniently divided into six more or less distinct classes, as 

 follows : central-spindle fibers, mantle fibers, polar fibers, con- 

 tractile fibers, cone fibers, and the retractile fibers of the spin- 

 dle cones. With the exception of the contractile fibers, which 

 possibly may be of archosomal nature, all the others are de- 

 cidedly of cytoplasmic origin ; none can be shown to be of 

 nuclear origin. All these various kinds of fibers stain in 

 about the same manner, readily taking the congo stain, with 

 the exception of the contractile fibers, which retain the iron- 

 haematoxylin longer than any of the others, and thus under 

 proper treatment appear quite dark, even by their color indicat- 

 ing a different origin. Their structure is also from the begin- 

 ning different, showing distinct beads. We will now consider 

 each of these classes more in detail. 



Mantle Fibers, Polar Fibers, and Central- Spindle Fibers. 



As these fibers have the same origin and otherwise resemble 

 each other they may most conveniently be considered together. 

 The central-spindle fibers are the first ones to appear during 

 the radiosomic process. As the two centrioles, with their 

 somospheres, move apart, there appear between them two 

 darkly staining, narrow threads which apparently help to push 

 the archosomes apart. Between these two threads the lighter 

 staining central-spindle fibers begin to appear, but only after 

 the centrosphere has separated in two parts, one to each archo- 

 some (Figs. 37, 38). The central-spindle fibers thus originate 

 from the outer edge of the centrosphere, just as do the polar 

 fibers and the mantle fibers. But while the polar fibers and 

 the mantle fibers are fed only from the cytoplasm proper, the 

 central-spindle fibers receive, almost at once, material from 

 the granosphere. At a very early stage we see numerous 

 rays projecting from the archosome to the granosphere, and 

 this radiation is so arranged and limited that, on the side 



