ON FECUNDATION, MATURATION, AND FERTILISATION. 319 
Phallusia mammillata. 
I studied the maturation and fertilisation of the ova of this 
Ascidian, partly with a view to comparing the origin of and 
the rdle played by the centrosomes with what I had found to 
be the case in the egg of Spherechinus, but more especially to 
compare the case of Phallusia with that of Styelopsis described 
fairly recently by Julin (5). The method employed was pre- 
cisely similar to the one already given for Sphzerechinus, 
A mixture of 90 to 95 per cent. saturated solution of corrosive 
sublimate with 10 to 5 per cent. glacial acetic was found in 
both cases to be the best preservative when followed by Hei- 
denhain’s iron hematoxylin stain. 
Here again I took no account of the changes to be observed 
in the living egg. These were sufficiently described by Stras- 
burger (7) so long ago as 1875. 
The ova were examined by means of sections in the ovary, 
oviduct, unfertilised after leaving the parent’s body, and after 
fecundation. Unfortunately with regard to the development 
of the ova I can give no details. I never succeeded in getting 
satisfactory preparations of the nuclear figures of the ovogones 
whilein the germinative zone. (I use Boveri’s (1) nomencla- 
ture in his well-known diagram of the sexual cells of Ascaris.) 
I can therefore give no such details as described by Julin 
for Styelopsis. Although I obtained preparations showing 
karyokinetic division in the ovaries of very young Ascidians, 
yet the cells themselves were so small that counting the 
chromosomes was impossible. I found precisely the same 
difficulty with the testes. 
Transverse sections of the ovary show ovogones in various 
stages in the zone of growth. The nucleus is relatively of 
enormous size, is vesicular, and contains a large circular 
“nucleolus” of chromatin (fig. 8). As the egg passes into 
the branches of the oviduct, the nucleus begins to get smaller, 
and lessens so quickly in size that it becomes hardly one 
sixth of its original diameter. The nucleolus disappears, the 
chromatin is more regularly dispersed in the form of a long 
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