461 
The Conjugation of the Infusoria . 
The other accomplishes the spore-formation and reduction, 
but only two of the spores produced atrophy (c). The other 
two in each individual form four like gametes by two fissions, 
and of these gametes two only are of functional use (d). The 
other two abort (d). After the conjugation, owing to the 
peculiar manner in which the macro-nuclei of new individuals 
are developed — in a mode quite different from that in which 
they arise in P. aurelia (a form also with two micronuclei) — 
1st. fission 
there is again a nuclear atrophy (£*). This is obviously due 
to the fact that, after the first virtual fission subsequent to 
conjugation, the one nucleus is specialised to form micro-nuclei, 
the other to give rise to macro-nuclei only. To the species as 
it at present exists, the one macro-nuclei-forming element has 
become superfluous, but, though useless, like so many abortive 
vestigial structures, it must still invariably be formed, because 
the useful and functional one could not otherwise arise. 
The form just considered presents quite sufficient com- 
ic k 
