336 SYDNEY J. HICKSON. 



state what stimulus there is that causes two individuals 

 to begin the sexual proceeding. It may be that some 

 excitement may be caused by the touching or brushing of the 

 arms, but nothing of the kind has been observed. Judging 

 from the development of the conjugative processes alone, 

 whicli is all that we have to guide us in the initial stages, it 

 seems probable that tlie sexual stimulus affects the two 

 individuals simultaneously, and that there is no differentiation 

 of sex. 



The Micronuclei. 



It is an interesting fact that, notwithstanding the careful 

 and elaborate investigations made by several observers on 

 the micronuclei of the Ciliata, there is at present no satis- 

 factory account of these structures in the Acinetaria. 



That micronuclei do occur in all Acinetaria is not yet proved, 

 but nevertheless it is extremely probable that they are as 

 constant a feature of the anatomy of this group of animals as 

 they appear to be of the Ciliata, 



In Biitschli's great work on the Infusoria (p. 1878) the 

 following notes will be found on the subject, Biitschli him- 

 self in 1867 discovered a micronucleus in a species of Sphae- 

 rophrya. Maupas proved with certainty the existence of a 

 micronucleus in Tokophrya limbata, Acineta tuberosa, 

 Podophrya fixa, and Podophrya cyclopum. He pro- 

 bably, but not with certainty, found them also in Acineta 

 Jolyi, whilst certain bodies which may have been micro- 

 nuclei were seen in Ephelota gemmipara. In Toko- 

 phrya limbata Mobius also proved the existence of micro- 

 nuclei. 



In a recent paper on the anatomy of a new species of 

 Ephelota, Ishikawa writes with some uncertainty about the 

 existence of micronuclei. The most satisfactory figures of 

 the micronuclei of Acinetaria are those given by Keppen (15), 

 but as his monograph is written in the Russian language I 

 am unable to read it. 



The authors of the 'Traite technique de Zoologie ' (5) accept 



