SEX DETERMINATION IN DINOPHLLUS GYROC1LIATUS. 347 
when a solution in distilled water was employed. There is 
little difference in the results obtained with sublimate-acetic 
or nitric, except that in the latter the sections are not so 
granular. I have made a very extensive trial of all the good 
fixatives in an endeavour to improve on the above reagents, 
but without success. A fixing fluid that has given fair results 
next to sublimate-nitric is a slight modification of Eisen’s 
iridium chloride solution. All the osmic and picric acid 
mixtures give but medium results, especially the picric acid 
ones, which are invariably poor. In the following work, there- 
fore, I have relied almost entirely on the results obtained with 
sublimate-nitric and acetic, and Perenyi’s solutions. 
There is considerable difference in the histological appearance 
of a section fixed with sublimate-nitric and that with PerenyPs 
solution. The general appearance of the section is much 
better in that fixed with Perenyi, while the histological 
details are shown much clearer in that fixed with sublimate. 
This is shown by the comparison of figs. 21 and 32 with 
fig. 42. Figs. 21 and 32 are from sections of material fixed 
in sublimate-nitric, while fig. 42 is from Perenyi’s solution. 
It will be seen that although the section drawn in fig. 42 
appears in general better fixed than that of fig. 32, there is 
nevertheless more shrinkage of the nuclear details in fig. 42 
than in that of fig. 32, and this is more marked on comparing 
the actual sections themselves. 
A reagent that I have found most useful in investigating 
the early oogenesis is aceto-carmine. With the use of this 
fixative and stain, it is possible to follow the early process of 
fertilisation from a whole preparation with great convenience. 
Figs. 13, 20 and 24 are drawn from such preparations. 
In sectioning the eggs I have found the most convenient 
method is to cut them, when fastened, to bits of amyloid 
liver. Another method consists in allowing some hard 
paraffin to cool in a watch glass and then cutting a small 
hole in this; the eggs, which are in zylol or cedar oil, are then 
carefully transferred into this with a line pipette and the 
excess of oil got rid of as much as possible. The paraffin is 
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