158 REPRODUCTION. 



readily reproduced. Salamanders even possess the faculty 

 of reproducing parts of the head, including the eye with all 

 its complicated structure. Something similar takes place in 

 our own bodies, when a new skin is formed over a wound, 

 or when a broken bone is reunited. 



332. In some of the lower animals, this power of repara- 

 tion is carried much farther, and applies to the whole body, 

 so as closely to imitate fissiparous reproduction. If an earth- 

 worm, or a fresh-water polyp, be divided into several pieces, 

 the injury is soon repaired, each fragment speedily becoming 

 a perfect animal. Something like this reparative faculty is 

 seen in the vegetable kingdom, as well as the animal. A 

 willow branch, planted in a moist soil, throws out roots below 

 and branches above ; and thus, after a time, assumes the 

 shape of a perfect tree. 



333. These various modes of reproduction do not exclude 

 each other. All animals which propagate by gemmiparous 

 or fissiparous reproduction also lay eggs. Thus the fresh- 

 water polyps (Hydra) propagate both by eggs and by buds. 

 In Vorticella, according to Ehrenberg, all three modes are 

 found ; it is propagated by eggs, by buds, and by division. 

 Ovulation, however, is the most common mode of reproduc- 

 tion ; the other modes, and also alternate reproduction, are 

 only additional means employed by Nature to secure the per- 

 petuation of the species. 



SECTION II. 



ALTERNATE AND EQUIVOCAL REPRODUCTION. 



334. It is a matter of common observation, that individuals 

 of the same species have the same general appearance, by 

 which their peculiar organization is indicated. The trans- 



