The Nucleolus and Microchromosomes in the Spermatogenesis etc. 187 
Out of anotlier 100 counts of Ist. meiotic 
90^ gave 15 gemini and tlie nucleolus. 
‘^% n over 15 ,, ,, ,, ,, 
7^ „ under 15 „ ,, „ „ 
Out of 100 counts of 2nd. meiotic 
91^ gave 15 chromosomes. 
6^ ,, over 15 ,, 
3^ „ under 15 „ 
Of the Ist. meiotic counts, only tliose cells were counted where 
the nucleolus was plainly visible, and could he distinguished from 
the gemini, and it will be seen that 88^ show 15 gemini. The 
rest, over and under 15 gemini were obviously cells so cut by the 
microtome as to exclude, or which had sliced the two ends of some 
gemini. 
The 2nd. meiotic also show 15 chromosomes in over 90^. Now 
it is evident that if the body which I have identified as a nucleolus, 
and which is included in the nucleus of one half the daughter cells 
of the Ist. meiotic division, were not a nucleolus but a chromosome, 
it ought to be seen in 50^ of the spindle figures of the 2nd. meiotic 
division. 
But as I have said before, all the nucleoli have completely dis- 
appeared by the time the 2nd. meiotic spindle has formed, and this 
fact together with the counts given above, proves conclusively that 
the nucleolus of the Ist. meiotic phase, is, in spite of its similarity 
to the gemini in its shape and behaviour, really a nucleolus, and 
not a chromosome, bivalent or nnivalent. 
Foot and Strobell (’07), in their able paper on Änasa tristis, 
have already disproved the existence in that Hemipteron of a hetero- 
tropic chromosome, which should behave as described by Wilson 
(’05). They have shown that there is a chromosome which they 
identify with Wilson’s heterotropic, which lags a little in its division, 
but it divides in both divisions, and is bivalent in the Ist. Their 
beautiful photographic illustrations also make it very plain that 
Wilson misinterpreted the true nucleolus of the prophase for an early 
condition of the heterotropic chromosome. 
Up to the formation of the 2nd. meiotic spindle, there is a great 
similarity in the behaviour of the nucleolus of the Ist. meiotic divi- 
sion in Hijdrophüus, and the body which Wilson calls the hetero- 
