340 ON THE NUMBER OP POLAR BODIES AND 



with the aid of our modern highly efficient appliances, they have 

 been found *. 



A deeper insight into the process of fertilization has above all 

 led to a closer study of antecedent phenomena. 



O. Hertwig 2 and Fol 3 showed that the formation of polar bodies 

 was connected with a division of the nuclear substance of the egg. 

 Hertwig and Biitschli 4 then proved that the body expelled from 

 the egg possessed the nature of a cell, and thus led the way to the 

 view that the formation of polar bodies is a process of cell-division, 

 although a very unequal one. Even then there was no reason for 

 attaching any special importance to the number of these bodies ; 

 nor should we have such a reason if we agreed with Minot 5 , Bal- 

 four 6 , and van Beneden in ascribing a high physiological signifi- 

 cance to this process, and assumed that the expelled polar body 

 is the male part of the previously hermaphrodite egg-cell. AVi- 

 should not know in what proportion the quantities of the ' male ' 

 and ' female ' parts were present, and it would therefore be impossible 

 to decide, a priori, whether the ' male ' part had to be removed 

 from the body of the egg-cell in one, two, or more portions. 



Even after the view that the nuclear substance is the essential 

 element in fertilization had gained ground a view chiefly due to 

 Strasburger's investigations on the process of fertilization in Pha- 

 nerogams and after Hertwig's opinion had been confirmed, that 

 the process of fertilization is essentially the conjugation of nuclei, 

 even then there appeared to be no reason why the numler of 

 divisions undergone by the nucleus of the mature egg should be 

 looked upon as an essential feature. 



1 The most recent example of this kind is afforded by the excellent work of 

 O. Schultze, ' Ueber die lieifung und Befruchtung des Amphibieneies,' Zeitschr. f. 

 wisa. Zool., Bd. XLV. 1887. Schultze has proved that two polar bodies are expelled 

 from the egg of the Axolotl and of the frog, although all previous observers, including 

 O. Hertwig, had been unable to find them. Thus the latter authority states as the 

 result of an investigation specially directed towards this point, that the nucleus is 

 transformed in a peculiar manner (' Befruchtung des thierischen Eies,' III. p. 81). 



" O. Hertwig, ' Beitrage zur Kenntniss der Bildung, Befruchtung, und Theilung 

 des thierischen Eies,' Morpholog. Jahrbuch, I, II, and III. 1875-77. 



3 H. Fol, ' Recherches sur la fecondation et le commencement de I'henogenie chez 

 divers animaux.' Geneve, Bale, Lyon, 1879. 



4 Biitschli, Entwicklungsgeschichtliche Beitrage,' Zeitschr. f. wise. Zool. I'.d. 

 XXIX. p. 237. 1877. 



* C. S. Minot, 'Account, etc.' Proceedings Boston Soc. Nat. Hist., vol. xix. p. 165. 

 1877. 



* F. M. Balfour, 'Comparative Embryology.' 



