270 LAY SERMONS, ESSAYS, AND REVIEWS. [xin. 



In favour of this hypothesis, Professor Kolliker adduces the 

 well-known facts of Agamogenesis, or &quot; alternate generation ; &quot; 

 the extreme dissimilarity of the males and females of many 

 animals ; and of the males, females, and neuters of those insects 

 which live in colonies : and he defines its relations to the 

 Darwinian theory as follows : 



u It is obvious that my hypothesis is apparently very similar to Darwin s, 

 inasmuch as I also consider that the various forms of animals have pro 

 ceeded directly from one another. My hypothesis of the creation of 

 organisms by heterogeneous generation, however, is distinguished very 

 essentially from Darwin s by the entire absence of the principle of useful 

 variations and their natural selection : and my fundamental conception is 

 this, that a great plan of development lies at the foundation of the origin 

 of the whole organic world, impelling the simpler forms to more and more 

 complex developments. How this law operates, what influences determine 

 the development of the eggs and &erms, and impel them to assume con 

 stantly new forms, I naturally cannot pretend to say ; but I can at least 

 adduce the great analogy of the alternation of generations. If a Bipinnaria, 

 a Brackiafaria, a Pluteus, is competent to produce the Echinoderm, which 

 is so widely different from it ; if a hydroid polype can produce the higher 

 Medusa : if the vermiform Trematode nurse can develop within itself the 

 very unlike Cercarla, it will not appear impossible that the egg, or ciliated 

 embryo, of a sponge, for once, under special conditions, might become a 

 hydroid polype, or the embryo of a Medusa, an Echinoderm.&quot; 



It is obvious, from these extracts, that Professor Kblliker s 

 hypothesis is based upon the supposed existence of a close 

 analogy between the phenomena of Agamogenesis and the 

 production of new species from pre-existing ones. But is the 

 analogy a real one ? We think that it is not, and, by the 

 hypothesis, cannot be. 



For what are the phaenomena of Agamogenesis, stated 

 generally ? An impregnated egg develops into an asexual form 

 A ; this gives rise, asexually, to a second form or forms, B, more 

 or less different from A. B may multiply asexually again ; in 

 the simpler cases, however, it does not, but, acquiring sexual 

 characters, produces impregnated eggs from whence A once more 

 arises. 



No case of Agamogenesis is known in which, when A differs 

 vndely from B, it is itself capable of sexual propagation. No 

 case whatever is known in which the progeny of B, by sexual 

 generation, is other than a reproduction of A. 



