58 



ANDREWS. 



seem to repeat in minute the characters of the whole area, for 

 they are surrounded by a pellicle of similar formation to the 

 nuclear pellicle, and they contain yet other areas of the same 

 kind as themselves, and these even others, so that the whole 

 nuclear area is a very complexly differentiated foam. 



Within the small spheres appear peculiar optical and physi- 

 cal modifications of the interalveolar substance, in the form of 

 minute very highly refractive and dense masses. This is the 

 "chromatin" substance. It is seen in greatest quantity in 

 one, two, or even three of the largest spherical areas, but is 

 sometimes found also in very small quantities in several others, 

 or in one only, according to stage of maturation. 



Two or more of the largest spheres, which contain the most 

 of this substance, approach and coalesce with each other, until 

 there is formed one sphere far larger than any of the others, 

 and now optically very distinct also, because of the amount of 

 the refractive chromatin it carries. 



Some of the smaller areas break up and disappear from time 

 to time, and so the whole nuclear area undergoes a thorough 

 and continuous series of redistributions of its elements, many 

 of these changes being carried on simultaneously. 



The largest sphere becomes the egg nucleus which after- 

 wards receives the sperm. Within it also, until the nuclear 

 membrane is dissipated, goes on a ceaseless shuffling of the 

 elements ; the smaller spherical areas being thus changed into 

 a more uniform arrangement which is bounded by the single 

 pellicular membrane, and the chromatin substance being dis- 

 posed in a seemingly continuous line of interalveolar material 

 which forms the nuclear optical network. I believe that the 

 rearrangements of the nuclear elements are continuous, and 

 that there is never what may be termed a truly resting or 

 quiescent stage. The phenomena become at times simply less 

 obvious, that is all. 



Even after dissipation of the nuclear membrane, and after 

 perfecting of the new nucleus, so far as one can trace the facts, 

 there remain small portions of the chromatin scattered about, 

 or massed together, in the nuclear substance, and later in the 

 cytoplasm. The presence of these was first noticed at Wood's 



