338 REPORT— 1894. 



APPENDIX. 



I. — On the ' Reduction Division ' in the Cartilaginous Fishes. 

 By J. E. S. Moore. 



In availing myself of the unrivalled opportunities for investigation 

 offered by the marine laboratory at Naples, I had in view the continua- 

 tion of some researches, concerning the nature of the origin of the repro- 

 ductive elements in forms which it was difficult to obtain under suitable 

 conditions "while at home. 



No great amount of reliable descriptive matter relating to the origin 

 and anatomy of the reproductive cells is really available from a modern 

 cytological standpoint ; but notwithstanding this paucity of material 

 wherewith to build, the intellectual activity of tlie time has been able 

 to fit it to a vast superstructure of speculation which in the minds of not 

 a few observers of to-day has only been built to fall. 



AVherever theory far outstrips the facts, and by its own light pene- 

 trates where actual observation has not yet been made, its explanations 

 are always subject to a long and close revision, as the bricks of the 

 actually known mount up and their theoretical substitutes are individually 

 weighed and left to stand or thrown away as wanting. 



The demonstration of a number of nuclear chromosomes constant for 

 each species both for animals and plants was no sooner found to be a 

 uniA^ersal truth than the discovery of a reduction by one half of this 

 number in the origin of the two pronuclei, as described by Hertwig in 

 the case of Ascaris, led up to the belief that in this phenomenon lay the 

 secret of that blending of hereditary characters which naturalists had so 

 long sought in vain. 



In the case of the invertebrates in which the reduction divisions were 

 first described, the chromosomes are said to pass undivided to the 

 daughter cells in such a way that there are only half as many in these 

 as in the parent, and the assumed universality of this phenomenon forms 

 the keynote of that part of Weismann's theory which deals with the 

 balancing of the hereditary stuffs at fertilisation. Some experience of 

 the phenomenon of maturation in the spermatogenesis of Mammalia had 

 convinced me that, although there was a numerical chromatic reduction, 

 this phenomenon was brought about in a manner quite different from 

 what was generally supposed ; and I determined during my stay in 

 Naples to study the same phenomena as pi-esented in Elasmobranchs, 

 so that we should be able to arrive at definite conclusions in another 

 great group of vertebrates. 



It had been my intention at the same time incidentally to make an 

 embryological study of the developmental liistology of the whole repro- 

 ductive gland, but the limited amount of material available for this 

 purpose necessitated the restriction of my work to somewhat narrower 

 lines. 



A preliminary account of this was published in the ' Anatomische 

 Anzeiger,' in a note ' On the Germinal Blastema and the Nature of the 

 so-called " Reduction Division " in the Cartilaginous Fishes,' which I had 

 completed on February 28. During March, April, and May I was able 

 to revise and extend the results I had hitherto obtained. 



It will be seen that my observations respecting the reduction phe- 

 nomena fit in admirably with the half theoretical »nticipations of Boveri, 



