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CHAPTER XXXVI. 



ON GENERATION. FISSIPAROUS MULTIPLICATION. GEMMIPAROUS 



MULTIPLICATION. TRUE GENERATION. METAMORPHOSIS. ME- 

 TAGENESIS, OR ALTERNATION OF GENERATIONS. SEXUAL ORGANS. 



INVERTEBRATA. INFUSORIA. POLYPS. ACALEPKLE. ECHINO- 



DERMATA. ENTOZOA. ANNELIDA. MOLLUSCA. CRUSTACEA. 



INSECTA. PISCES. REPTILTA. AVES. MAMMALIA. 



AMONGST the lower classes of organised beings, both in the 

 animal and vegetable kingdom, the multiplication of individuals, 

 or the propagation of the species, is provided for by three different 

 processes, while in the highest forms of animal life the process of 

 generation is restricted to one of these types. 



The simplest manner in which the multiplication of individuals 

 takes place, consists in the division of the being into two, each of 

 these again dividing into two others, and so on ; this is multipli- 

 cation by fission. 



The second mode of increase consists in the formation of a bud 

 at some part of the body of the parent : this bud is gradually 

 developed, drops off, becomes independent of its parent, and ulti- 

 mately assumes a perfect form, resembling in all particulars that 

 from which it sprung. 



The third mode differs materially from the two former, in 

 the fact, that the new organism results from a series of changes 

 occurring in an impregnated ovum, which is produced by the 

 mutual action of the contents of two dissimilar cells, the products 

 of distinct parental organs. The new body differs essentially from 

 either of the two cells which produced it. This is true generation. 



Fissiparous Multiplication. In the lowest plants, such as the 

 lichens and fungi, this mode of multiplication very commonly 

 occurs. The cell, or cells, of which the plant consists, divide and 

 sub-divide; and, in this manner, new organisms are produced. 

 The same mode of reproduction is also seen to be very common 

 amongst the Infusoria, and may be watched in the common 

 vorticella. 



