116 COMPARISON OF VEGETABLE 



discover that they are furnished with any enve- 

 lope. In the course of a few months these gem- 

 mules enlarge in size, each assuming an oval or 

 pear-like shape, and are then seen projecting 

 from the sides of the internal canals of the pa- 

 rent, to which they adhere by their narrow ex- 

 tremities. In process of time, they become de- 

 tached, one after the other ; and are swept along 

 by the currents of fluid, which are rapidly pass- 

 ing out of the larger orifices." * " When two 

 gemmules, in the course of their spreading on 

 the surface of a watch-glass, come into contact 

 with each other, their clear margins unite with- 

 out the least interruption, in a few days we 

 can detect no line of distinction between them, 

 and they continue to grow as one animal. The 

 same thing happens, according to the observa- 

 tions of Cavolini, to adult sponges, which on 

 coming into mutual contact, grow together, and 

 form an inseparable union. In this species of 

 animal grafting we again find an analogy be- 

 tween the constitution of zoophytes and that of 

 plants." f 



81. With respect to the higher orders of ve- 



* Roget, Anim. and Veget. Physiol. p. 156. 

 t Ib. p. 159. 



