VI. 



ON THE NUMBER OF POLAR BODIES AND 

 THEIR SIGNIFICANCE IN HEREDITY. 



I. Parthenogenetic and Sexual Egg. 



Hitherto no value has been attached to the question 

 whether an animal egg produces one or two polar bodies. 

 Several observers have found two such bodies in man}^ 

 different groups of animals, both high and low in the scale of 

 organization. In certain species only one has been observed, 

 in others again three, four, or five (e. g. Bischoff, in the rabbit). 

 Many observers did not even record the number of polar 

 bodies found by them, and simply spoke of ' polar bodies.' 

 As long as their formation was looked upon as a process of 

 secondary physiological importance— as an ' excretion,' or a 

 'process of purification,' or even as the 'excreta' (!) of the egg, 

 as a ' rejuvenescence of the nucleus.' or of mere historical 

 interest as a reminiscence of ancestral processes, without any 

 present physiological meaning — so long was it unnecessary to 

 attach any importance to the number of these bodies, or to paj^ 

 special attention to them. Of all the above-mentioned views, 

 the one which explained polar bodies as a mere reminiscence 

 of ancestral processes seemed to be especially well founded. 

 Ten years ago we were far from being able to prove that polar 

 bodies occurred in all animal eggs, and even in 1880, Balfour said 

 in his excellent ' Comparative Embryology,' ' It is very possible, 

 not to say probable, that such changes [the formation of polar 

 bodies] are universal in the animal kingdom, but the present 

 state of our knowledge does not justify us in saying so^' 



Even at the present day we are not, strictly speaking, 

 justified in making this assertion, for polar bodies have not yet 

 been proved to occur in certain groups of animals, such as 

 reptiles and birds ; but they have been detected in the great 



' Vol. I. p. 60. 



