42 An Introduction to Zoology. 



power, to repleuisb nature by the production of a constant succession of 

 like forms j and thus while the individuals perish, to preserve the species 

 permanent. 



Besides the specific and universally analogous mode of reproduction in 

 vegetables, by seed "after their kind," and inanimals by the like provision 

 of eggs 3 we have moreover in the vegetable kingdom, and also in some of 

 the lowest members of the animal kingdom, which closely border upon the 

 former, and are therefore termed zoophytes, (animal plants) two subordi- 

 nate methods of multiplication ; the first of these is in fact multiplication 

 by division, and is called fissiparous reproduction j thus we propagate 

 plants by cuttings, each detached slip ultimately becoming a complete 

 plant, like that from which it was taken. In the lower members of the 

 animal kingdom, the infusory animalcules, polypi, the planaria (a vermi- 

 form race, approaching in structure to the annelida, or annular worms,) 

 in some species of the annelida, and in the star-fish tribe, if we cut up the 

 animals into various segments, each segment will reproduce the wanting 

 parts, and re-form itself into a complete animal. The questions of indi- 

 viduality and personal identity in those species, might puzzle the most 

 acute metaphysician. In the Crustacea, this power becomes restricted to 

 the partial reproduction of single detached limbs ; and in higher animals, 

 to the occasional reproduction of bony matter and the like. 



Another mode of reproduction is that of vegetables by buds j the bud, 

 in fact, is a nascent individual, with all the original properties and struc- 

 ture of the parent stock, but destined in plants, unless artificially sepai-ated, 

 to remain attached to that j)arent stock, which thus presents (as do many 

 of the zoophytes) a composite being.* If artificially detached, it will of 

 course, as in the former method of propagation by slips, give rise to a 

 complete plant ; and its development will be exactly similar, whether it 

 grows in tlie ground, or is still united to the original stock whence it sprang. 

 There is a close connection between this and the following method of pro- 

 pagation by seed, for a seed is in efiect nothing but a bud intended to be 

 detached, and necessarily to commence a course of separate existence, and 

 therefore provided with a store of nutriment essential to its first develop- 

 ment. But whereas, in the case of the seed, we are allowed to observe a 

 previous process carried on in the faecundating organs of the flower essential 



* The subject of these composite animals is perhaps the branch of physiology 

 whicb has as yet received the least sufficient elucidation. It is especially to be re- 

 gretted that Dr. Roget, in his admirable Bridgevvater Essay, has treated it so briefly, 

 and entirely omitted all mention of the most extraordinary class of composite ani- 

 mals, which belong to an higher order than the Zoophytes, and closely approximate 

 to the bivalve mollusca, (though devoid of shells) the composite Ascidise, the subject 

 of a monograph by Savigny, assuredly one of the most valuable of Zoological Essays. 

 We hope in a future number to return to this subject, and to have some oiiginal in- 

 formation to produce in its illusti-ation. 



