4.26 PHILOSOPHY OF ZOOLOGY. 
milar mode of propagation has been observed among the 
Nereidz and Planariz. 
Doubts have been reasonably entertained whether this 
is a natural mode of propagating individuals. Exuis de- 
livers his opinion on the subject with little hesitation. “ The 
proportion, (says he), of the number of the animals which 
I have observed to divide in this manner, to the rest, is 
scarce 1 to 50; so that it appears rather to arise from 
hurts received by some few ammalcula among the many, 
than to be the natural manner in which these kinds of animals 
multiply ; especially if we consider the infinite number of 
young ones which are visible to us through the transparent 
skins of their bodies, and even the young ones that are vi- 
sible in those young ones, while in the bodies of the old 
ones *.” The multiplication of individuals by artificial di- 
vision, countendnces such an opimion. ‘The common Hy- 
dra, which is naturally gemmiparous, may be cut into two 
or more parts; and each detached portion, by repairing 
the wound, and supplying what is defective, will, in a short 
time, become a perfect animal. Such divisions are similar 
to slips or grafts in the vegetable kingdom; and al- 
though they obviously are merely extensions of an indivi- 
dual, yet, by acquiring new organs, and becoming capable 
of exercising distinct volitions, they acquire an identity pe- 
cular to themselves. ‘They are multiplications of indivi- 
duals at least, and, consequently, serve the same purposes 
as the products of those other modes of generation which 
have been regarded as more perfect +. They afford very 

* Phil. Trans. 1769, p. 143. 
+ Many respectable botanists and horticulturists of the present day ap- 
pear to regard all plants produced from cuttings, layers, roots or buds, as 
extenstons merely of those plants to which they originally belonged, and as 
being influenced, in reference to their duration, by circumstances different 
