4 
W. E. AGAE. 
Methods. 
All the observations were made on testes fixed either with 
Flemming (strong formula) or corrosive-acetic. For more 
than a year I used ordinary paraffin sections, mostly 10 ji in 
thickness, and mostly stained with Heidenhain’s iron-alum 
hematoxylin and eosin. Then the whole was worked through 
again with celloidin sections, 35-40 jj. in thickness, which are 
thick enough to contain whole nuclei, untouched by the 
razor. In order to reduce to a minimum the possibility of a 
disarrangement of the chromatin by the processes of cutting 
and mounting the sections, in the great majority of cases 
these sections were mounted without dissolving out the 
celloidin. In most cases the tissue was stained in bulk with 
Ehrlich's hsematoxylin before embedding, though it is 
possible to stain the sections after cutting. Unless the 
celloidin is dissolved away, however, the latter method has 
the disadvantage of diminishing the transparency of the 
sections owing to the celloidin taking up some of the stain. 
The sections were mounted between two coverslips instead of 
between a slide and a coverslip, so as to allow of the nuclei 
being examined from both sides. The optical apparatus 
employed was largely Zeiss' stereoscopic eyepiece, generally 
used in conjunction with an oil-immersion objective. This 
method is one which I found of the utmost value. Firstly, 
one can be certain that all the chromosomes are present and 
in their natural positions. Secondly, the nucleus can be 
examined and drawn from both sides and the chromosomes 
identified in the two drawings. In this way it is often 
possible to analyse a clump of chromosomes which otherwise 
could not have been separated, and the danger of overlooking 
a chromosome which is overlaid by another is removed. This 
is specially valuable in a form like Lepidosiren, where the 
chromosomes are large and rather numerous. The two views 
of the same nucleus obtained in this way are shown in PI. 4, 
fig. 26, which illustrates the value of the method. Thirdly, the 
stereoscopic eyepiece is an immense help (as a supplement to 
