426 PHILOSOPHY OF ZOOLOGY. 



milar mode of propagation has been observed among the 

 Nereidae and PlanariaB. 



Doubts have been reasonably entertained whether this 

 is a natural mode of propagating individuals. ELLIS 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 animalcula 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, countenances such an opinion. The common Hy- 

 dra, which is naturally gemmiparous, may be cut into two 

 or more parts ; and each detached portion, by repairii'o; 

 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 a! - 

 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- 

 culiar 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. 



f Many respectable botanists and horticulturists of the present day ap- 

 pear to regard all plants produced from cuttings, layers, roots or buds, a;> 

 extensions merely of those plants to which they originally belonged, and as 

 being influenced, in reference to their duration, by circumstances different 



