i 7 4 AGE, GROWTH, AND DEATH 



direction of Professor Hubrecht, the principal student 

 of the development of this type of animal. Here, 

 No. i, we can see an early stage in which the germ 

 consists of but a single cell, and at this point is the 

 nucleus. Note its size and then compare it with the 

 nuclei in No. 2, in which several of these cells, as 

 they appear in a section, are represented. The cells 

 themselves are now smaller because they have multi- 

 plied by the division of the original germ, but the 

 nuclei in them are likewise smaller ; and in the older 

 stage, No. 3, where the number of cells has begun 

 still further to increase, we see that there is another 

 and more marked reduction in the size of the nuclei. 

 Contrast the single nucleus of the early stage with 

 the small nuclei of the later one, and notice how very 

 striking is the change in the size. Thus, during the 

 early development of Tarsius, we find that there is 

 an actual rapid reduction in the size of the nucleus. 

 That the nuclei become smaller during the segmenta- 

 tion of the ovum may be asserted safely to be a 

 general law. I have examined a large number of 

 publications in which the segmentation of representa- 

 tives of the principal classes of the animal kingdom 

 is figured. Without exception the drawings of all 

 the authors show the fact, but very rarely have I 

 found even an allusion in the text to the progressive 

 alteration in the diameters of the nuclei. The only 

 author known to me who has explicitly recognised 

 the invariable occurrence of the change, and who has 

 clearly emphasised its importance, is Professor Richard 



