Spindle Lengths in Spermatocyte Metaphases of Helix pomatia. 193 



and both have given excellent results. The latter, which affects the 

 cytoplasm as well as the chromatin, enables spindle fibres to be seen very 

 distinctly ; and all drawings on the plate have accordingly been made from 

 sections thus stained. In the case of the iron hematoxylin, the slides were 

 placed for four hours in the mordant, which was an aqueous solution of 

 ferric' alum, and were then stained for 12 hours ; in the case of the iron 

 brazilin, the slides remained for two hours in a solution of ferric alum in 

 70-per-cent. alcohol, and were then placed in the stain for 15 hours. 



The preparations were studied with a Zeiss apochromatic oil-immersion 

 objective of 2 mm. focus and N.A. 1"30, and compensating oculars ISTos. 4, 6, 

 12, and 18. The light was obtained from an inverted incandescent gas 

 burner, and was passed through a Gifford screen and the holoscopic oil- 

 immersion substage condenser of Messrs. Watson and Sons, of London. All 

 drawings were made with a large Abbe camera lucida at one magnification, 

 which was estimated with a stage micrometer graduated to read one- 

 hundredth part of a millimetre. Possible distortion was prevented by 

 levelling the microscope platform and drawing table ; and, in order to 

 minimize error due to foreshortening, measurements have been made only of 

 spindles of which the major axes lay at right angles to the microscopic line of 

 vision, i.e. spindles of which the centrosomes could be brought into focus 

 simultaneously. I have tried to eliminate inaccuracy of draughtsmanship 

 by drawing the centrosomes of each spindle many times and upon several 

 occasions ; moreover, the lengths found by me have been checked by 

 independent measurements made by my assistant, Mr. Eussell Goddard. 



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

 Spermatocyte Metaphase. 



Fig. 1 of the plate represents a polar view of the primary spermatocyte 

 complex. I have not attempted to count the chromosomes on the various 

 spindles ; but recent investigations seem to show that the number is 48 in 

 the spermatogonial and 24 in the spermatocyte cells. The chromosomes are 

 short thick rods, and do not differ from one another greatly in size. 



Figs. 2 to 12 inclusive are drawings of lateral views of the spindle at the 

 conclusion of this metaphase ; in each figure constriction of the chromosomes 

 is seen to have been completed, and the daughter rods, apposed to one 

 another in the equatorial plane, are ready to move apart. These drawings 

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

 hermaphrodite glands of several individuals, and the length of the spindle is 

 the same in all. This length has been found in every primary spermatocyte 

 cell studied at this stage, and, at the known magnification, represents 15"3 fi. 



