THE RELATION OF LIFE TO OTHER FORCES. 307 



Life manifests itself by Birth, Growth, Development, Decline and 

 Death; and an idea of life will most naturally arise by taking these events 

 in succession, and studying them individually, and in relation to each 

 other. 



When the embryo in a seed awakes from that state, neither life nor 

 death, which is called dormant vitality, and, bursting its envelopes, 

 begins to grow up and develop, it may be said that there is a birth. 

 And so, when the chick escapes from the egg, and when any living form 

 is, as the phrase goes, brought into the world. In each case, however, 

 birth is not the beginning of life, but only the continuation of it under 

 different conditions. To understand the beginning of life in any indi- 

 vidual, whether plant or animal, existence must be traced somewhat 

 farther back, and in this way an idea gained concerning the nature of the 

 germ, the development of which is to issue in birth. 



The germ may be defined as that portion of the parent which is set 

 apart with power to grow up into the likeness of the being from which it 

 has been derived. 



The manner in which the germ is separated from the parent does not 

 here concern us. It belongs to the special subject of generation. Neither 

 need we consider apart from others those modes of propagation, as fission 

 and gemmation, which differ more apparently than really from the or- 

 dinary process typified in the formation of the seed or ovum. In every 

 case alike, a new individual plant or animal is a portion of its parent: it 

 may be a mere outgrowth or bud, which, if separated, can maintain an 

 independent existence; it may be not an outgrowth but simply a portion 

 of the parent's structure, which has been naturally or artificially cut off, 

 as in the spontaneous or artificial cleaving of a polype; it may be the 

 embryo of a seed or ovum, as in those cases in which the process of mul- 

 tiplication of different organs has reached the point of separation of the 

 individual more or less completely into two sexes, the mutual conjugation 

 of a portion of each of which, the sperm-cell and the germ-cell, is necessary 

 for the production of a new being. We are so accustomed to regard the 

 conjugation of the two sexes as necessary for what is called generation, 

 that we are apt to forget that it is only gradually in the upward progress 

 of development of the vegetable and animal kingdoms, that those portions 

 of organized matter which are to produce new beings are allotted to two 

 separate individuals. In the least developed forms of life, almost any 

 part of the body is capable of assuming the characters of a separate indi- 

 vidual; and propagation, therefore, occurs by fission or gemmation in 

 some form or other. Then, in beings a little higher in rank, only a 

 special part of the body can become a separate being, and only by conju- 

 gation with another special part. Still, there is but one parent; and this 

 hermaphrodite-form of generation is the rule in the vegetable and least 

 developed portion of the animal kingdom. At last, in all animals but 



