310 LAY SERMONS, ADDRESSES, AND REVIEWS. [xiil 



they may be, in the strictest sense, the descendants, was 

 subjected ? 



It will be obvious from what has preceded, that we 

 do not agree with Professor Kolliker in thinking the 

 objections which he brings forward so weighty as to be 

 fatal to Darwin's view. But even if the case were other- 

 wise, we should be unable to accept the " Theory of 

 Heterogeneous Generation ; ' which is offered as a sub- 

 stitute. That theory is thus stated : — 



" The fundamental conception of this hypothesis is, that, under the 

 influence of a general law of development, the germs of organisms 

 produce others different from themselves. This might happen (1) by 

 the fecundated ova passing, in the course of their development, under 

 particular circumstances, into higher forms ; (2) by the primitive and 

 later organisms producing other organisms without fecundation, out of 

 germs or eggs (Parthenogenesis)." 



In favour of this hypothesis, Professor Kolliker ad- 

 duces the well-known facts of Agamogenesis, or " alter- 

 nate generation ; " 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 : — 



" 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 proceeded 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 germs, and impel them to assume constantly 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 Brachi- 

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

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



