On Spermatogenesis in the Rat. 
By 
Herbert H. Brown, 
University College, London. 
With Plates XXII and XXIII. 
The following paper is the result of an investigation which 
I have made during the past year, in the Physiological Labo- 
ratory at University College, upon the spermatogenesis of the 
Rat, which, owing to the large size of its spermatozoa, and 
especially of the “ middle piece,” presents peculiar advantages 
for the purpose. Although minor points of difference exist 
(in the relative length of the “ middle piece ” of the sper- 
matozoon and in the shape of the “ head ”) the process is 
apparently in all essential points identical with that which 
occurs in other mammals, and hence may be taken as a type 
of “ mammalian spermatogenesis.” 
Methods of Research. — I have studied the process of 
spermatogenesis by means of sections, and by teased prepara- 
tions. 
(1) Sections prepared by the paraffin-shellac method from 
the testis gradually hardened in alcohol, i. e. by being placed 
in alcoholic solution of gradually increasing strength. The 
sections were prepared from small pieces of the organ, stained 
in bulk, by immersion in Kleinenberg’s alcoholic hsematoxylin 
solution for about three hours, the excess of stain being removed 
by acidulated alcohol, or by prolonged immersion (for a week) 
in a very dilute watery solution. From sections stained with 
VOL. XXV. NEW SER. Z 
