ALTERNATE AND EQUIVOCAL REPRODUCTION. 127 



happens with the arms of the star-fishes. The tail of a 

 lizard is also readily reproduced. Salamanders even pos- 

 sess the faculty of reproducing parts of the head, including 

 the eye with all its complicated structure. Something simi- 

 lar 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 be divided into several pieces, the injury is 

 soon repaired ; and if we cut in fragments a fresh-water 

 polyp, each one speedily becomes a perfect animal. Some- 

 thing 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 gemmipa- 

 rous 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 mode of re- 

 production that most generally prevails ; the others, and 

 also alternate reproduction, are additional means employed 

 by nature to secure the perpetuation of the species. 



SECTION II. 



ALTERNATE AND EQUIVOCAL REPRODUCTION. 



334. It is a matter of common observation, that individu- 

 als of the same species have the same general appear- 



