i66 AGE, GROWTH, AND DEATH 



volume of the egg is scarcely bigger than before ; and 

 such increased volume as has occurred has been due 

 to the absorption of some of the surrounding water. 

 In many animals not even this increase by the 

 absorption of water takes place. During the segmen- 

 tation of the ovum the condition of things has been 

 reversed so far as the proportions of nucleus and pro- 

 toplasm are concerned. We have nucleus produced, 

 so to speak, to excess. The nuclear substance is in- 

 creased during this first phase of development. H ence 

 our conclusion : Rejitvenation is accomplished chiefly 

 by the segmentation of the ovum. 



Naturally, as we embryologists looked upon these 

 things in earlier days and thought of the progress of 

 development, we conceived of the earlier stage as 

 younger, and of the ovum as being the youngest 

 stage of all, a conception which in terms of time is 

 obviously correct, but as regards the nature of the 

 development, it seems to me clearly, is not correct. 

 The ovum is a cell derived from the parent body, 

 fertilised by the male element, and presenting the 

 old state to us, the state in which there is an excessive 

 amount of protoplasm in proportion to the nucleus ; 

 and in order to get anything which is young, a process 

 of rejuvenation is necessary, and that rejuvenation is 

 the first thing to be done in development. The nuclei 

 multiply ; they multiply at the expense of the protoplasm. 

 They take food from the material which is stored up in 

 the ovum, nourish themselves by it, grow and multiply 

 until they become the dominant part in the structure. 



