180 BIOLOGY: GENERAL AND MEDICAL 



ance of all other forms of reproduction among the high- 

 est animals and plants. 



As we have found the reproductive power a charac- 

 teristic of living substance, so we find this power remain- 

 ing among otherwise differentiated multicellular beings 

 long after more simple forms have adopted sexual modes 

 of development. Even after the differentiation of so- 

 matic and germinal cells has been effected, and germinal 

 cells of two sexes established, the general tendency of 

 the cells toward reproduction remains strong and shows 

 itself in a variety of ways. 



Thus, among plants, long after sexual reproduction 

 has been established and even in certain forms in which 

 sexual organs and seeds are produced, the asexual form 

 of multiplication continues and may be the chief method 

 of reproduction. The garlics, for example, produce no 

 seeds, but only bulbs, and the banana, though it pro- 

 duces seeds, continues to grow chiefly through bulbous 

 buds. Other plants, Chara, with well-developed sexual 

 organs, produce but one, the female sex. 



Among animals, although the asexual mode of repro- 

 duction is chiefly confined to the protozoa, we find it 

 continuing among the ccelenterates and worms, both of 

 which multiply by gemmation though eggs are also 

 produced. 



In this particular the hydra is more lowly than the 

 sponges which multiply exclusively through eggs, 

 because it continues to multiply by buds as well as by 

 eggs. The buds appear upon the body wall as rounded 

 eminences, which in the course of time become pro- 

 vided with tentacles, come more and more closely to 

 resemble the parent, and finally separate themselves as 

 new individuals. In addition, however, certain of 

 the apparently undifferentiated cells of the ectoderm 

 increase locally in number forming gonads which con- 

 tain the germ cells, one group situated near the tentacles 

 being the homologue of the testes of the higher animals, 

 the other usually developed near the aboral end, forming 



