328 r. M. BALFOUR. 



extent this network extends into the yolk. I have never yet 

 seen the limits of it, though it is very common to see the 

 coarsest yolk-granules lying in its meshes. Some of these 

 are shoAvn in PI. XIII, fig. 2, y k. 



This network of lines ^ (probably bubbles) is characteristic 

 of many cells, especially ova. We are, therefore, forced to 

 believe that the fine granular and probably coarser granular 

 yolk of this meroblastic egg consists of an active organized 

 basis with passive yolk-spheres imbedded in it. The organized 

 basis is especially concentrated at the germinal pole of the 

 egg, but becomes less and less in quantity, as compared with 

 the yoke-spheres, the further we depart from this. 



Admitting, as I think it is necessary to do, the organized 

 condition of the whole yolk sphere, there are two possible views 

 as to its nature. We may either take the view that it is one 

 gigantic cellj the ovum, which has grown at the expense of the 

 other cells of the egg-follicle, and that these cells in becoming 

 absorbed have completely lost their individuality; or we may 

 look upon the true formative yolk (as far as we can separate it 

 from the remainder of the food yolk) as the remains of one cell 

 (the primitive ovum), and the remainder of the yolk as a body 

 formed from the coalescence of the other cells of the egg- 

 follicle, which is adherent to, but has not coalesced with, the 

 primitive ovum, the cells in this case not having completely 

 lost their individuality ; and to these cells, the nuclei, I have 

 found, must be supposed to belong. 



The former view I think, for many reasons, the most 

 probable. The share of these nuclei in the segmentation, and 

 the presence of similar nuclei in the cells of the germ, both 

 support it, and are at the same time difficulties in the way of 

 the other view. Leaving this question which cannot be 

 discussed fully in a preliminary paper like the present one, 

 I vnll pass on to another important question, viz. — 



How do these nuclei originate ? Are they formed by the 

 division of the pre-existing nuclei, or by an independent 

 formation. It must be admitted that many specimens are 

 strongly in favour of the view that they increase by division. 

 In the first place, they are often seen^two together;" examples 

 of this will be seen in PI. XIII, fig. 1. In the second place, I 

 have found several specimens in which five or six ajjpear 

 close together, which look very much as if there had been an 

 actual division into six nuclei. It is, however, possible in 

 this case that the nuclei are really connected below and only 



^ The interpretation of this network is entirely due to Dr. Kleinenberg, 

 who suggested it to me on my showing iiim a. number of specinieos cx« 

 hibiting the nuclei and network. 



