1879]. 199 *  {Minot. 
on the contrary at first senescence must rise in less than, afterwards 
faster than in, geometrical progression. As we have seen, senescence 
affects the different cells unequally, and accordingly some cells are 
dividing while others are not. In the mature body it appears that a 
minority of the cells are in process of division while the majority are 
not. ; 
At the time when senescence has nearly produced a cessation of 
growth, the animal is mature and the sexual products arise, and ac- 
complish the office of rejuvenation. The intimate connection of ma- 
turity and of the development of the eggs and sperma, must lead to 
the hypothesis of a causal connection which we can express by say- 
ing the exhaustion of the rejuvenating power becomes the stimulus for 
the formation of the sexual products. This view is very similar to the 
theory of rejuvenation among Infusoria, as brought forward by 
Biitschli in his work on the ‘‘ Eizelle.’’ Further interesting specu- 
lations suggest themselves, but where the phenomena themselves are 
so vaguely known, speculation is unsafe and must be renounced. 
The curve of growth evidently determines the size of the animal, for 
at the time when the rate of growth of the body in weight becomes 
zero, the animal has attained its maximum size. It appears to me a 
perfectly safe conclusion that in small animals the senescence gains 
the mastery quicker than in large animals; otherwise stated, that the 
juvenescence is less powerful in small than in large animals. More- 
over, although we have no very accurate knowledge as to the length 
of life of most animals, yet in a rough way we know that the larger 
.an animal the longer it lives; this confirms the idea that in large 
animals senescence proceeds more slowly than in smaller ones. The 
age and size of animals are thus brought into intimate correlation, 
but it does not follow that all animals of the same size live to the 
same age — this, if true, would oblige us to assume that the original 
frequency of the cell divisions, in other words the interval between 
impregnation and the first division of the yolk is always the same. 
We must on the contrary conceive that it is very unequal, so that 
though the senescence of the corresponding cell-generations of two 
species of the same mature size may be equal in quantity, yet in that 
species in which the original interval was greatest, the n” generation 
will come later and therefore that species will be the longer lived. I 
insert these remarks to avoid the possibility of conveying the im: 
