250 



spore formation and reduction, aborts (&) ^). The other accomplishes the 

 formation and reduction, but only two of the spores produced atrophy 

 (c). The other two in each individual from 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 



Pig. 4. 



// 



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) — there is again a 

 nuclear atrophy (g). This is obviously due to the fact that, after the 

 first virtual fission subsequent to conjugation, the one nucleus is 

 specialised to form micronuclei, the other to give rise to macronuclei 

 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 vestigeal structures, it must still invariably be found, 

 because the useful and functional one could not otherwise arise. 



The form just considered presents quite sufficient complications 

 in the processes which result in the building up of new individuals 

 after the conjugation, but in the next and final one (Vorticella, Fig. 5) 

 these are met with in a yet more exaggerated form, and other amaz- 

 ing things happen prior to the conjugation. The reader may be 



1) Abortion of virtual spore daughter-cells. 



