EEPRODUCTION 67 



they have been developing they at once again 

 divide in an approximately horizontal plane, so that 

 sixteen cells now make up the congeries. The 

 subsequent course of the development of these 

 shows that some of the cells with, of course, their 

 included nuclei, which would under normal circum- 

 stances have been worked up into one part of the 

 body, are, under the altered conditions, actually 

 converted into another. The significance of this 

 experiment will be obvious to any one who con- 

 considers it, but that significance will be increased 

 when it is remembered that the results negative 

 certain views which were held as to the specific 

 character of the nuclei. It was held by some that 

 the nucleus of each cell was of a specific character 

 and could produce a cell of one type and of one type 

 only. Even if this were the case it would not have 

 helped us very far along the road towards an ex- 

 planation of the powers of the cell, for we should 

 still be ignorant of how the nucleus succeeded in 

 so modifying the cell as to make it lead to the 

 development of a liver or of some other part of 

 the body. But this experiment, and many others 

 of a similar kind might be cited, seems to show 

 that the nuclei of the various cells during develop- 

 ment, at any rate, have no specific character, but 

 are capable, to put the matter colloquially, of 



