44, MARCUS M. HARTOG. 
view is that in conjugation the meganucleus undergoes a dis- 
organisation and is sometimes completely destroyed, while the 
pronuclei which conjugate are descendants of the micro- 
nucleus only. From the conjugation-nucleus is regenerated a 
complete nuclear apparatus in the exconjugates; rarely is even 
a part of the old meganucleus retained and utilised by con- 
crescence with the new one formed from the conjugation- 
nucleus. 
The details are singularly interesting. Two Ciliates approach 
as apparent gametes, and join by the ventral surface. Their 
meganuclei undergo fragmentation. The micronucleus in each 
enlarges and then undergoes three mitotic divisions; usually 
three of the four nuclei formed at the second division (which 
we may letter ,”) abort as rejection-nuclei (“‘ noyaux de 
rebut” of Maupas), and they degenerate and are excreted or 
digested ; while the fourth nucleus (yu?) divides to produce the 
two pronuclei (y°®). The only difference between the three 
abortive and the one preserved nucleus of the brood (yu?) is 
that of position ; it is the nucleus nearest the mouth of the 
gamete that produces the pronuclei. Again, the pronuclei 
are absolutely similar in all save position :—that nearer the 
mouth of the gamete passes over as a migratory pro- 
nucleus into the other gamete, the one more remote as a 
stationary pronucleus awaits the arrival of the migra- 
tory pronucleus from the other gamete. For convenience and 
by analogy we may term the migratory and the stationary 
gametes “male” and “female” respectively, but we must 
remember that there is no essential difference between them, 
and we shall find in Vorticellines, where the gametes fuse 
completely and only one zygote-nucleus is formed, that it is 
constituted by the union of two migratory nuclei. After 
the fusion of the pronuclei is complete the gametes separate. 
I give a schema of the processes in a single gamete up to this 
point (Fig. 6). 
