METAPHASE SPINDLE IN FOliLICULA AUlUCULARIA. 251 
plate at a magnification siicli that no doubt can exist concerning 
the stage of mitosis ; the second will show a lateral view of 
the two centrosomes at a lower magnification, from which the 
length of the spindle must be deduced. 
It is unlikely that these measurements will lead directly to 
an explanation of spindle formation ; but they may suggest 
some further generalisation, which will bring us one step 
nearer to the solution of this problem. 
Material and Methods. 
The material was collected in July, aud preserved in either 
Flemmiugis strong chromo-aceto-osmic acid fluid or the 
platiuo-aceto-osmic acid solution of Hermann. In an earlier 
paper I recommended the latter ; but for these studies, in 
which extreme transparency of the cytoplasm is essential, 
‘the former has undoubtedly given the better results. 
The testes were not dissected out until required for em- 
bedding; but the integument of the back was slit open 
to ensure immediate access of the fixative, in which the 
material remained for twenty-four or forty-eight hours. It 
was then washed in running water for twenty-four hours, 
and passed successively through 30 per cent., 50 per 
•cent, and 70 per cent, aqueous solutions of alcohol, remaining 
for four hours in each of the two first-named and for eight 
hours in the last. It was then stored in a solution of 80 per 
cent, alcohol. 
Latei-, the testes were placed in a 90 per cent, aqueous 
solution of alcohol for twenty-four hours, and then passed 
through a 95 per cent, solution, absolute alcohol, aud xylol ; 
after which they were embedded in paraffin having a 
duelting-point of 52° C. Sections were cut 8 fi thick with an 
ordinary Cambridge rocking microtome, and were stained 
on the slide. The mordant used was an aqueous solution of 
•iron alum, in which the sections remained for six hours ; 
they were then stained for fifteen hours in Heidenhain’s iron- 
Iisematoxylin, and the excess of colour was later washed out 
