THE BEGINNINGS OF LIFE. 



565 



' Which 



^ Was 



!C 



PNooi:- 



products. 



Id thus 

 of all 



)ees 



J 



These processes of <^ alternate generation' formerly 

 attracted very much attention, and were first pro- 

 minently brought under the notice of naturalists by 

 Steenstrup, in 1842 ^ Whether occurring amongst 

 animal or vegetal forms, the processes are essentially 

 characterized by the fact that a fertilized germ goes 

 through two or more metamorphic stages before at- 

 taining the perfect form in which similar fertilized 

 germs are evolved^ whilst in each of the lower stages 

 the immature forms possess the power of multiplying 

 agamically. By common consent such a succession of 

 forms is admitted to correspond to what is known as 

 an organic ^species/ The fact of the metamorphosis 

 could of course have no effect in negativing such a 

 view, seeing that it has hitherto afforded no obstacle 

 in the case of insects : although in instances of ^ alter- 

 nate generation/ a further complication, it is true, is 

 introduced by the fact of the multiplication which takes 

 be found anioiiss*f^! place amongst the lower metamorphic forms, and by the 



fact that the successive stages are occasionally mere 

 derivative forms produced by a process of ^gemmation/ 

 The fact of the multiplication of the transition forms, 

 however, cannot introduce any real difficulty, since a 



omena of 'afe 

 leemed to 

 tationl 



leceii't 



)des by which seiual t 

 ►>ie • Ephemeroffiorpk';- 



llv/ at long and altfi 



■ r 



stages 



> 



1 ver)- nidimentan t, 

 be found m4 ^'l 

 f this kind probaHi'f 

 as a possible fcl ^^■ 

 ne differentiatei 

 . later stages of '^'^ 

 ' .uch changes ^^ 



-^ ,, it #T 





^ 



heterogenetic germ is large, the organism develops without metamor- 

 phosis, and subsequently produces large germs or ova, which also go 

 through a similarly 'direct' process of development. Instances of this 

 occur amongst Nematoids and Rotifers, and probably also amongst 

 some Medusce, Trematodes, and other low forms of life. 



^ In his ' Generations-Wechsel,' of which a translation was published 

 by the Ray Society in 1845. 



