4 CLASSIFICATION AND ADAPTATION 



the better we can understand the sexual and parental 

 habits of different kinds of animals. 



The two branches of biological study which we 

 are contrasting cannot, however, be completely 

 separated even by those whose studies are most 

 specialised. In Bionomics it is necessary to dis- 

 tinguish the types which are observed, and often 

 even the species, as may be illustrated by the fact 

 that controversies occasionally arise among amateur 

 and even professional fishermen on the question 

 whether dog-fishes are viviparous or oviparous, the 

 fact being that some species are the one and others 

 the other, or the fact that the harmless slow-worm 

 and ring-snake are dreaded and killed in the belief 

 that they are venomous snakes. Taxonomies, on 

 the other hand, must take account of the sex of its 

 specimens, and the changes of structure that an 

 individual undergoes in the course of its life, and of 

 the different types that may be normally produced 

 from the same parents, otherwise absurd errors are 

 perpetrated. The young, the male, and the female 

 of the same species have frequently been described 

 under different names as distinct species or even 

 genera. For example, the larva of marine crabs 

 was formerly described as a distinct genus under 

 the name of Zoaea, and in the earlier part of the 

 nineteenth century a lively controversy on the 

 question was carried on between a retired naval 

 surgeon who hatched Zoaea from the eggs of crabs, 

 and an eminent authority who was Professor at 

 Oxford and a Fellow of the Royal Society, and who 

 maintained that Zoaea was a mature and inde- 

 pendent form. In the end taxonomy had to be 

 altered so as to conform with the fact of develop- 



