350 ON THE NUMBER OF POLAR BODIES AND [VI. 



majority of the large groups of the animal kingdom, and 

 wherever they have been looked for 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 ^ and Fol ^ showed that the formation of polar 

 bodies was connected with a division of the nuclear substance 

 of the ^gg. Hertwig and Butschli * then proved that the body 

 expelled from the ^gg 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^, Balfour'', and van Beneden 

 in ascribing a high physiological significance to this process, 

 and assumed that the expelled polar body is the male part of 

 the previously hermaphrodite egg-cell. We 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 

 Phanerogams — and after Hertwig's opinion had been confirmed, 



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

 work of O. Schultze, ' Ueber die Reifung und Befruchtung des Amphi- 

 bieneies,' Zeitschr. f. wiss. 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. 



^ H. Fol, '■ Recherches sur la fecondation et le commencement de 

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



* Butschli, ' Entwicklungsgeschichtliche Beitrage,' Zeitschr. f. wiss. 

 Zool. Bd. XXIX. p. 237. 1877. 



5 C. S. Minot, 'Account, &c.,' Proceedings Boston Soc. Nat. Hist., vol. 

 xix. p. 165. 1877. 



^ F. M. Balfour, •' Comparative Embryology.' 



