1892.] of the oosperm nucleus in certain ova. 17 



In many cases, however, where division of the nucleus is not 

 followed by division of the cell substance, we have amitotic division 

 of the nuclei. 



In the spermatogenesis of many animals for example, the nuclei 

 of the spermatogonia increase and multiply long before the pro- 

 toplasm segregates round them to form the cell substance of the 

 spermatogonia. 



In recent years we have fragmentation of the nucleus in sperma- 

 togenesis described by Verson in Bombyx. 



I can find no trace of mitotic nuclear division in the sperma- 

 togenesis of Alcyonium, Millepora, Distichopora and Allopora, 

 although by using the same stains I can demonstrate the karyo- 

 kinetic figures in the divisions of the spermatogonia of Ascaris 

 where segmentation of the cell protoplasm follows division of the 

 nuclei. 



Similarly Brandt was unable to find karyokinesis in the divisions 

 of the nucleus to form the nuclei of the spores in certain Radio- 

 laria, and Hertwig too describes a process of nuclear fragmentation 

 in the formation of the nuclei of the spores of Thallassicola. 



Many examples could be given of mitotic division of the nuclei 

 of giant cells, such as we find described in the marrow of bone by 

 Denys, inflammatory cells of the cornea and the spleen of the 

 white mouse by Arnold. 



All of these facts of histology tend to show that it is possible 

 that in those ova which do not regularly segment the oosperm 

 nucleus may fragment. 



I do not wish for one moment to say that it is definitely proved 

 that it does fragment in any one case, for it is never safe to 

 generalise upon purely negative evidence until every precaution 

 has been taken to eliminate all possible sources of error. 



In this case of Distichopora for example, we cannot say that 

 a karyokinetic figure does not occur in the first division of the 

 oosperm nucleus until a great variety of preservative reagents have 

 been experimented with ; but on the other hand, I think I have 

 shown sufficient reason to justify us in hesitating to accept the view 

 that seems to be only too prevalent at the present time that karyo- 

 kinesis must always occur in the first nuclear divisions of the 

 developing ovum. 



(3) Gynodioecism in the Lahiatoi. (Second paper.) By J. C. 

 Willis, B.A., Gonville and Caius College (Frank Smart Student). 



In a paper read on May 30th, 1892*, a short preHminary ac- 

 count was given of some observations and experiments upon this 

 subject. These observations have been continued during the 



* Proc. Camb. Phil. Soe. Vol. vii., Part vi., p. 349. 



VOL. VIII. PT. L 2 



