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 many 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 pay special atten- 

 tion 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 1 .' 



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 majority of the large groups 

 of the animal kingdom, and wherever they have been looked for 



1 Vol. I. P . 60. 

 z 3 



