POLAR GLOBULE. 355 



firmed by more recent observations. The deformation and 

 -gyration of the vitellus have been observed in ova before fe- 

 cundation, and have nothing to do with the process of de- 

 velopment. They are of the class of movements called 

 amoeboid. 



After the penetration of spermatozoids and their union 

 with the vitellus, at least in many of the lower orders of ani- 

 mals, the appearance of the vitellus undergoes a remarkable 

 change, by which ova that are about to pass through the first 

 processes of development may be readily distinguished from 

 those which have not been fecundated. This change consists 

 in an enlargement of the granules and their more complete 

 separation from the clear substance of the vitellus. The 

 granules then refract light more strongly than before, so that 

 the fecundated ova are distinctly brighter than the others. 1 

 This is the first appearance that is distinctive of fecundation. 



Polar Globule. The next process observed in the ovum 

 is the separation from the vitellus of a comparatively clear, 

 rounded mass, called by Robin the polar globule. This body 

 had been observed before by various anatomists and described 

 under different names. The exact mode of its formation has 

 been studied by Robin in some of the lower orders of ani- 

 mals. 3 We shall describe briefly this process as it was de- 

 monstrated to us by Robin in the ova of the Limnaeus stag- 

 nalis, in 1861, the description being taken from notes made 

 at that time : 



Five hours after the entrance of the spermatozoids, we 

 see a little elevation at one point in the vitellus. This is the 

 beginning of the polar globule. It increases in size gradu- 

 ally, and becomes constricted at its base, until it is attached to 

 the vitellus by a little pedicle. There is then, usually, a sec- 

 ond globule formed just behind the first, in the same man- 



1 ROBIN, Memoire sur les phenome'nes gui se passent dans Vovule avant la seg- 

 mentation du vitellus. Journal de la physiologie, Paris, 1862, tome v., p. 108. 



2 ROBIN, Memoire sur les globules polaires de I'ovule. Journal de la physiolo- 

 gie, Paris, 1862, tome v., p. 149, et seq. 



