398 F, M. BALFOUR. 



permanent ova i^rnflually increase in size. The following table 

 gives the diameter of four such nuclei : — 



0022 mm. 

 0-022 mm. 

 0-02i mm. 

 0032 mm. 



These figures should be compared with those of the table on 

 pag(^ 396. 



The ova when first formed are situated either at the surface 

 or in the deeper layers of the germinal e})ithelium. Though to a 

 great extent surrounded by the ordinary cells of the germinal 

 epithelium, they are not at first enclosed in a definite follicular 

 epithelium. The follicle is, however, very early formed. 



My observations lead me then to the conclusion that in a 

 general way the permanent ova are formed by the increase of 

 protoplasm round some of the nuclei of a nest, and the sub- 

 sequent separation of the nuclei with their protoplasm from the 

 nest as distinct cells — a mode of formation exactly comparable 

 with that which so often takes place in invertebrate egg tubes. 



Besides the mode of formation of permanent ova just de- 

 scribed, a second one also seems probably to occur. In ovaries 

 just younger than those in which permanent ova are distinctly 

 formed, there are present primitive ova, with modified nuclei of 

 the stellate variety, or nuclei sometimes even approaching in 

 character those of permanent ova, which are quite isolated 

 and not enclosed in a definite nest. The body of these ova 

 is formed of granular protoplasm, but their outlines are very 

 indistinct. Such ova are considerably larger than the normal 

 primitive ova. They may measure O-Oi mm. In a slightly 

 later stage, when fully formed permanent ova are present, 

 isolated ones are not infrequent, and it seems natural to 

 conclude that these isolated ova are the direct descendants 

 of the primitive ova of the earlier stage. It seems a fair de- 

 duction that in some cases primitive ova undergo a direct 

 metamorphosis into permanent ova by a modification of their 

 nucleus, and the assumption of a granular character in their 

 protoplasm, without ever forming the constituent part of a 

 nest. 



It is not quite clear to me that in all nests the coalescence 

 of the protoplasm of the ova necessarily takes place, since some 

 nests are to be found at all stages in which the ova are distinct. 

 Nevertheless, I am inclined to believe that the fusion of the ova 

 is the normal occurrence. 



The mode of formation of the permanent ova may then, accord- 

 ing to my ol)servati()us, take place in two ways : — 1. By the forma- 

 tion of granular protoplasm round the nucleus in a nest, and the 



