AND THE LOWER ANIMALS. 277 



and that it tends incessantly to render structures more 

 perfect. 



Doubtless, in attaining the essential, the accessory 

 is frequently sacrificed, and the latter appears to be 

 the case to an almost excessive degree in the recurrent 

 development of certain animals. In these instances, 

 too, more than in any others, the truth of the general 

 law we have been laying down is apparent. For 

 example, in the Lernea the entire body becomes 

 deformed and atrophied to the advantage of a single 

 apparatus ; but the function which this apparatus has 

 to perform is the perpetuation of the species. Hence 

 it is the most important one, and as soon as its dis- 

 charge commences, all the others are, so to speak, 

 absorbed by it, doubtless from the circumstance that 

 the animal is incapable of supporting all. 



Apart from the apparent exceptions of the preced- 

 ing instance, the character of the metamorphosis is 

 of a most striking nature. When an animal, which un- 

 dergoes simple transformations, has its development 

 arrested at any stage, a monstrosity is produced, as 

 the result of that circumstance alone. As to animals 

 with geneagenesis and metamorphosis properly so 

 called, their larvae and scolices are always incomplete 

 beings ; they are true first sketches, which are ren- 

 dered more and more perfect at each developmental 

 phase and each new evolution, till the primitive type 

 makes its appearance. 



Metamorphosis — simple transformation in the more 

 perfect animals — becomes more complex in proportion 

 as we approach the lower divisions of the animal 

 kingdom. Metamorphosis properly so called is quite 

 exceptional among the vertebrates. It is only 



