ALTEENATE AND EQUIVOCAL EEPEODUCTION. 341 



above ; and thus, after a time, assumes the shape of a perfect 

 tree. 



515. 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 For- 

 ticella, according to Ehrenberg, all three modes are found ; it 

 is propagated by eggs, by buds, and by division. Ovulation, 

 however, is the common mode of reproduction, the other modes, 

 and also alternate reproduction, are only additional means 

 employed by nature to secure the perpetuation of the species. 



SECTION II. 



ALTEENATE AND EQUIVOCAL EEPEODUCTIQN. 



51G. 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 transmis- 

 sion of these characteristics, from one generation to the next, 

 is justly considered as one of the great laws of the animal and 

 vegetable kingdoms. It is, indeed, one of the points on which 

 the definition of species is generally founded. We would, 

 however, adopt the new definition of Dr. S. G. Morton, who 

 defines species to be "primordial organic forms." 



517. But it does not follow that animals must resemble 

 their parents in every condition, and at every epoch of then* 

 existence ; on the contrary, as we have seen, this resemblance 

 is very faint in most species at birth, and some undergo com- 

 plete metamorphoses before attaining their final shape, such 

 as the caterpillar and the tadpole, the butterfly and the frog. 

 Nevertheless, we do not hesitate to refer the tadpole and the 

 frog to the same species ; and so with the caterpillar and the 

 butterfly, because we know that there is the same individual 

 observed in different stages of development. 



518. There is also another series of cases in which the 

 offspring not only do not resemble the parent at birth, but 

 moreover remain different during their whole life, so that their 

 relationship is not apparent until a succeeding generation. 

 The son does not resemble the father, but the grandfather; and 

 in some cases the resemblance reappears only at the fourth or 

 fifth generation, and even later. This singular mode of re- 

 production has received the name of alternate generation. 



