
972 The American Naturalist. [November, 
\ 
ON THE QUANTITY AND DYNAMICS OF 
ANIMAL TISSUES. 
BY J. LAWTON WILLIAMS. 
VERY ONE knows that the animal tissues are not fixed and 
unvarying quantities. From the time of an animal’s first 
appearance in the outer world to that of its disappearance by the 
natural processes of dissolution it exhibits many morphological 
changes, so obtrusive as not to require comment. They are spoken 
of as developmental changes, and are often so radical and 
thoroughgoing that the later forms in the series bear no resem- 
blance to their antecedent forms. Such are the total metamor- 
phoses of certain insects, crustaceans, worms, and sponges. Partial 
metamorphoses are gone through even by the highest types, so 
that the adult form often possesses morphological characteristics 
which are not present in the young, or vice versa. But there are 
other less obvious changes which affect the tissues, and are not so 
easily studied by direct observation. Such are the changes in 
quantity arising from varying rates of nutrition and other dis- - 
turbing causes. Besides these fluctuations, which are directly 
referable to immediate causes, there are others which appear to be 
constitutional, and proceed along definite paths of development 
throughout the lifetime of the animal. Moreover, these less 
apparent changes seem to adhere to animal species with much the 
same persistency that the more ostensible outward differences do. 
That is to say, just as one can distinguish an adult deer from its 
young by change in the form of its antlers, so, if he were a 
thorough expert, he could detect equally important changes in its 
internal parts which might serve as the basis of distinctions just 
as important as the ones here employed. In the absence of any 
extended investigations, it is impossible to speak with quantitative 
exactness of the inner changes from the time of birth to the 
attainment of old age. Such a record upon any one animal would 
: be impossible from the very fact that the first investigation would : 
ce n the animal of life. To conduct intelligent experiments 



