Variations in the Animal Kingdom. 11 



We will now consider the question of true variation, by which 

 I mean the deviation from the normal type in consequence of 

 some perfectly natural condition, which condition, however, is, 

 from some cause, different from that to which the varying species 

 has become adapted ; or else some condition or conditions which, 

 though to a certain extent artificial, do not in any way interfere 

 with the chief life functions of the species in question. 



Mr. Herbert Spencer has defined life as that in which an 

 organism is in perfect correspondence with its environments or 

 the continuous adjustment of internal relations to external rela- 

 tions. A good illustration of this is the case of a man and a 

 fish. Both live by breathing oxygen, but one breathes by means 

 of lungs and the other by means of gills. If, therefore, the one 

 breathing by lungs exchanged places with the one breathing by 

 gills, both would cease to live, because neither would in that 

 case be in correspondence with its environment ; or, in other 

 words, there would be a violent interruption in the continuous 

 adjustment of their internal to their external relations. On 

 the other hand, however, if the correspondence with the environ- 

 ment can be kept up by a modification of one or the other, or 

 both, or if the adjustment of the internal with the external rela- 

 tions can be effected, then life is not extinguished, but a varia- 

 tion takes place, and existence goes on upon a different basis. 

 For example, it has been recorded that a lizard {Axoletus, I 

 beheve), breathing in water by means of brauchiaB, by being 

 gradually weaned, so to speak, from its aquatic life, became 

 perfectly terrestrial, and lost its branchi^ altogether. For such 

 a thing to occur in one individual is remarkable, and helps to 

 show what might take place through a long series of generations 

 under varying conditions of existence. 



I will divide the few observations I have to make into two 

 sections for convenience, viz., variation of form or structure, and 

 variation of colour and markuigs. As to the former, I will begin 

 with a very common mollusc, the observation on which I have 

 already briefly described before this Club ; but before doing so I 

 should like to say a word or two as to the terms common or rare 

 as applied to any organism. It must be borne in mind that 

 these terms are very general, and must not be taken to mean 

 exactly what they seem to ; for if any species became really rare, 

 it follows that it must rapidly become extinct. No doubt many 

 species occur in far greater profusion than others, but on the 

 other hand, many so-called rarities exist also in profusion, but 

 out of the reach of man. This applies chiefly to marine 

 organisms, Crustacea, Mollusca, &c. ; and, as an illustration, I 

 will mention two iustauces of my own experience. The large 

 bivalve, Mactia r/lauca, has always been quoted as a great rarity 

 by authorities, even in the Channel Islands, where I found it. 



