LIMITS OF DIVISIBILITY or LIVING MATTER 331 



determining the limits of divisibility of living matter, it is of 

 importance to decide whether such a pluteus arises from a 

 piece of an egg the mass of which amounts also to one- 

 eighth of that of the total egg. We must therefore know 

 whether the embryos originating from fragments of an egg 

 grow more rapidly or more slowly than those which arise 

 from an entire egg. Now, as I have mentioned before, it is 

 a general rule that the smallest pieces after having attained 

 the blastula stage develop less rapidly than those which are 

 formed from an entire egg. In my earlier experiments on 

 growth and regeneration in Tubularia I found that develop- 

 ment and growth are functions of the same variables ; there 

 can be no doubt that to a certain extent development is only 

 a function of growth. It is therefore probable that the 

 embryo arising from a small fragment of an egg grows less 

 rapidly than that arising from an entire egg. It is therefore 

 also probable that a pluteus the mass of which amounts to 

 only one-eighth of that of a normal pluteus has developed 

 from a fragment of an egg which contained more than one- 

 eighth of the substance of the entire egg. I will, however, 

 not deny the possibility that a later observer may perhaps 

 find a still smaller pluteus, even though the large number of 

 my experiments renders this scarcely probable. 1 But I 

 believe that even in such a case the limit which I have given 

 will suffer no great reduction. The divisibility of the egg is 

 therefore very limited, if one demands that the fragment 

 shall develop into a pluteus. 



6. So far as my present experiments are concerned, I am 

 not yet able to say where the limits of divisibility lie, when 

 it is only required that the piece develop into a blastula. 

 The tiniest pieces of isolated egg-protoplasm still divided if 



i Boveri has since stated that he found a pluteus whose linear dimensions were 

 only one-third of those of a normal pluteus of the same culture. But as a slight 

 retardation in the growth of the arms may easily lead to such a result, I think that, 

 on the whole, the limits observed by me in many experiments will be nearer the tr th 

 than the one exceptional observation made by Boveri. [1903] 



