38 PHILOSOPHY OF ZOOLOGY. 
are not connected with the skeleton, but produced by the 
skin, and differ in nothing but shape from the nails of the 
fingers or toes. Where such excrescences have been ob- 
served on sheep, they have resembled the substance of the 
hoof *. 
In all these different instances of monstrosity, in the Ami- 
mal Kingdom, (and many similar cases might have been 
enumerated,) in which certain organs perform functions 
which are unnatural to them, we still find limits assigned 
even to these aberrations. 'The new parts, how extraordi- 
nary soever they may appear, are still similar to the parts 
of some other portion of the system. The organs which 
characterise one species, are never produced on other spe- 
cies as monstrosities ; so that there is no mixture or trans- 
mutation. The functions of a system may thus be deran- 
ged, and the harmony of its parts destroyed ; but to such ir- 
regularities there are bounds which are never exceeded +. 
These occurrences, which take place during the conti- 
nuance of life, serve greatly to shorten its duration. Neither 
dwarfs nor giants survive the usual period of existence. The 
attainment of the senile «véavaci, so anxiously wished for 
by all, only takes place when there is an equilibrium be- 
tween all the organs; when each organ exercises its own 
peculiar actions; and when the body escapes the destruc- 
tive influence of external accidents. Previous to the disso- 
lution of the fabric, we witness a rigidity of the vessels; a 
deficiency of the fluids; and a cessation of motion. The 
vital principle then deserts the body which it has construct- 

“ See Sir Everann Home’s “ Observations on Horny Excrescences of the 
Human Body.”—Phil. Trans. 1791, vol. Ixxxi. p. 95.-105. 
+ The reader will find some short but pertinent remarks on this sub- 
ject, by Dr Barcuay, “ On the Causes of Organization.”—Memoirs of the 
Wernerian Natural History Society, vol. ii. part. 2. p. 537.-546. 
