b CAPT. C. F. U. MEEK ON THE 



alum has no effect upon the former, but this cannot be said o£ the alcohol ; 

 so great care must be taken not to wash out the whole of the plasma 

 stain in the subsequent process of dehydration through successive strengths 

 of alcohol. The iron hsematoxylin gives the best results in all cases where it 

 is required to bring the chromosomes and nucleoli into evidence ; and this 

 is particularly noticeable when camera-lucida drawings are needed. Davis 

 obtained his best results with iron hsematoxylin in (conjunction with bordeaux- 

 red, and has confined himself almost entirely to this combination. 



When staining with safranin I used a 50 % solution in alcohol, leaving the 

 slides in it for from twelve to twenty-four hours ; this gives an orange-grey 

 tint to the protoplasm, the chromatin staining bright red. Henneguy's 

 method is a modification of this, for the safranin used is made by 

 Zwaardemaker's formula, being a mixture of equal volumes of alcoholic 

 safranin and anilin water : the slides were placed for five minutes in a 

 50/0 aqueous solution of permanganate of potassium, which acts as a mordant, 

 and then stained for six or twelve hours, after careful washing in running- 

 water. The excess of colour was removed by a high strength of alcohol. 

 Wilcox used this method when working upon Caloptenus femur-ruhrum, and 

 obtained good results ; he however allowed the slides to remain in the stain 

 only for a few minutes. 



In the iron brazilin method, first described by Hickson *, no second stain is 

 necessary, for the cytoplasm as well as the chromatin is affected : the slides 

 were placed for two or three hours in a solution of iron alum in 70 7o alcohol, 

 and were then stained for from sixteen to twenty-four hours. This stain is 

 useful for studying late stages of unripe spermatozoa and their earlier 

 spermatid transformations. 



The tricolor stain of Flemming gives very delicate results, particularly in 

 stages other than those of actual mitosis.' I stained in safranin for forty-eight 

 hours, and washed the superfluous colour out with strong alcohol ; the slides 

 were then taken down to water through successive strengths of alcohol, and 

 were stained for several hours in an aqueous solution of gentian, after which 

 they were washed in water and placed for ten minutes in a similar solution 

 of orange Gr, which acts as a differentiating agent for the gentian. This 

 combination gives a purple tint to the chromosomes and nucleoli, the spindle 

 fibres, &c., appearing in various shades of grey and brown. 



The Follicles of the Testis. 



The testes are two ovoid paired organs lying dorsally to the alimentary 

 canal in the middle of the abdomen, and so closely associated that they can 



* Hickson, S. J., ''Staining with Brazilin," Quart. Journ. Micr. Sci. xliv. p. 469, 1901. 



