i8g6. THE MEANING OF METAMORPHOSIS. 401 



a stage, although the fuH-grown forms of this family are not 

 usually considered as pre-eminently the most complex of the first 

 series of orders ? 



Mr. Miall uses a purely Darwinian phraseology, in part of his 

 paper, in speaking of the generally earlier transformations of the 

 inhabitants of shallow seas as contrasted with the later occurring and 

 supposed " adult transformations " of Amphibia and Insecta. " It 

 is," he says, " often of advantage that there should be division of 

 labour between the several stages of the life-history, and the functions 

 of migration and growth may be allotted to special times of life 

 instead of being carried on throughout." " Marine animals commonly 

 produce far more eggs than insects. The risks of the shallow seas 

 are so great that a small proportion only of the young animals come 

 to maturity." That is to say, if we correctly understand the 

 argument, the inference is that these differences between marine 

 animals and the inhabitants of the fresh waters and land have arisen 

 through natural selection. So also in the following: — "The more 

 sluggish and sedentary the adult, the greater the activity we may 

 expect to find in the larvae. It is they that have to travel and find 

 suitable quarters." 



This appears to us as assuming as proved the question just now 

 at issue in the world of science. Is a habit or a structure of any 

 special advantage, and, if so, what effect has it upon the life of the 

 species and the possible origin of varieties, and other species ? Can 

 these structures have arisen from other causes than natural selection ? 

 Everything that is suitable must in one sense be advantageous, but 

 the fact, that any structure is of advantage, does not prove that this is, 

 or even may have been, the cause either of its suitability or of its 

 origin or anterior existence. It is of advantage, and it is also 

 extremely suitable to its surroundings, that a drop of rain is 

 spherical, but both of these adjustments to the surroundings are the 

 results of laws that govern the relations of fluids to the earth and its 

 atmosphere. 



Natural selection resting on the often unproved assumption of the 

 advantage of this or that structure is, in most of its supposed applica- 

 tions, to our minds untrue, and when it is true it is a result and not a 

 cause. For example, with reference to the last quotations from Professor 

 Miall, a vast number of Protozoa are very active, and we are not 

 aware that they have very sluggish young, nor yet that their methods 

 of reproduction differ essentially, or that they produce young which 

 are any less volatile than those borne of sedentary forms. It is true 

 that Porifera, Hydrozoa, Actinozoa, Vermes, and most of the Inverte- 

 brata that are aquatic have numerous eggs and very active larvae as 

 compared with the parents ; but it is also worth while to consider 

 whether this may not be due to the fact that these all belong to groups 

 having a certain structure which may have been acted upon in a 

 certain way by their surroundings. 



