194 Mr. C. F. U. Meek. TJie Ratio between Spindle 



In the circumstances we have reason for believing that the length of the 

 spindle is a constant at the conclusion of the primary spermatocyte metaphase. 



The Length of the Mitotic Spindle at the Conclusion of the Secondary 

 Spermatocyte Metaphase. 



■ Kg. 13 represents a polar view of the equatorial plate in this metaphase. 

 The chromosomes are noticeably smaller than those of the preceding cell 

 generation. 



Figs. 14 to 23 inclusive are drawings of lateral views of the spindle at 

 the conclusion of tbe metaphase, i.e. at the moment when constriction of 

 the chromosomes is complete. As in the case of figs. 2-12, these drawings 

 have been made at a magnification of 650 diameters from sections in the 

 hermaphrodite glands of several specimens. The length of the spindle, 

 estimated from the magnification, is invariably 12 - 1 /x; and, since the centro- 

 somes have been found to be equidistant in all secondary spermatocyte cells 

 studied at this stage, we seem again to be dealing with a constant. 



The Ratio between the Lengths of the Mitotic Spindle at the Conclusion of the 

 Primary and Secondary Spermatocyte Metapliases. 



I have already remarked that in Forficula auricularia the ratio between 

 the lengths of the mitotic spindle at the conclusion of the two spermatocyte 

 metapliases is almost identical with the ratio between the radii of two 

 spheres of which the volume of one is equal to twice that of the other. The 

 former ratio is 1"28 : TOO, and the latter ratio is T26 : TOO. 



Now the lengths of the spindle found for the conclusion of these meta- 

 phases in Helix pomatia are 15 - 3 and 12 - 1 respectively, and the ratio 

 between them is T26 : TOO. Xo period of growth separates the primary and 

 secondary spermatocyte mitoses in this organism ; the connection between 

 spindle length and cell volume is therefore again suggested. 



The accuracy of my measurements seems to be confirmed by the work of 

 Demoll. In a paper published last year upon the spermatogenesis of Helix 

 pomatia, he gives two drawings respectively representing the lengths of the 

 mitotic spindle in the primary and secondary spermatocyte metaphases. We 

 are not told at what stage of the metaphase these drawings were made, nor 

 is the magnification mentioned ; but the lengths shown are 29 - 7 and 24 - mm., 

 and the ratio between them is T24 : TOO. Demoll. however, appears to have 

 seen no possible significance in these relative lengths ; for he dismissed 

 the matter by saying that the length of the spindle decreases only slightly 

 when the cell volume is halved. 



