SOME PROBLEMS OF REPRODUCTION. 47 
indeed, the fact that cytoplastic division remains in abeyance 
during the absence of a meganucleus in “ working order” is an 
additional argument for regarding this as a directive organ. 
We may note that the pairing individuals are in many cases 
much reduced below the normal size by a rapidly repeated 
series of bipartitions. 
We may then briefly state our view of the homologies of the 
process of conjugation thus:—(1) The three mitoses of the 
micronucleus point to a primitive formation of gametes in 
broods of eight. (2) The fact that no cell division accompanies 
these mitoses may be the physiological result of the inertness 
of the now disorganised meganucleus. (3) The formation of two 
fertile pronuclei in each gamete points to an ancestral stage, in 
which a binary division of two mutually attached individuals 
immediately preceded the conjugation of their offspring. (4) The 
interchange of pronuclei and separation of the gametes are 
probably modifications of the process indicated in (3), directed 
to the preservation of the highly organised cytoplast. (5) 
The pairing Ciliata before the completion of the preliminary 
mitoses are not true gametes, but progametes. 
b. Vorticellinea. 
The group of VortTicELLINEs, consisting of attached forms, 
is exceptional in two respects. (1) The conjugating indi- 
viduals, instead of being similar, are unlike and unequal; the 
larger individual being of the ordinary attached type, the 
smaller free, and produced by repeated vertical fissions from 
an ordinary individual. (2) Instead of the gametes separating 
ultimately, they fuse, the larger absorbing the smaller into 
itself; and of the four pronuclei which are formed as in other 
Ciliates, only two unite to form a single conjugation-nucleus. 
The preliminary mitoses and formation of rejection-nuclei 
offer no exceptional character, save that in the male two 
micronuclei are formed (indicating a further suppressed fis- 
sion). Two pronuclei are formed in either gamete, and the 
migratory pronuclei, instead of passing one another, fuse 
where they meet ; while the stationary pronuclei both abort. 
