130 BEITISH APHIDES. 



II.— BIOLOGY AND MORPHOLOGY OF 

 APHIDES. 



1.— GENERAL OBSERVATIONS. 



It may be said that Aristotle initiated the science 

 of biology, when he detailed the observations con- 

 tained in his Hist. Animalium and in his Be Partlbus. 

 Amongst other things, he made the acute observation 

 that the young cuttle carried its own yolk-sac, for 

 some time after birth, protruding from its mouth ; 

 and that drones apparently were produced from unfer- 

 tilised eggs. 



As biology may be considered to be the science 

 which comprehends life in all its branches and rela- 

 tions ; so we may severally regard physiology as the 

 science which treats of function, morphology the science 

 which deals with development and form, phytogeny the 

 genealogy of tribes, and ontology the history of germs. 



In discussing this last section Prof. Haeckel urges 

 that philosophic reflection ought to have equal value 

 with what he calls empiricism, that is, scientific experi- 

 ment. In other terms, that philosophy and experiment 

 should blend.* Much here will depend on the definition 

 we may give to the term "philosophy," in order that 



* If these threads be blended, they must not be confounded. The 

 caution of some of our early thinkers in separating general laws from 

 hypothesis may be shown by the following remarks of Euler and 

 Laplace. The former says : 



'• Laws may not be enunciated upon insufficient experience." Thus he 

 shows that *' scr + a t -\-41 up to the 40th term produces a prime number, 

 that is, a number incapable of an exact division by a smaller number. 

 Let a* = any number less than 41 ; then, if multiplied by itself, and 

 added t<> itself, and added to 41, the number is non-divisible; by which 

 it Dlighi be inferred thai ;i law had Keen discovered. Such experience, 

 however, is erroneous ; as the next term so treated gives a divisible 

 number." 



Laplace says, in introducing his famous theory, " I present this 

 hypothesis with the distrust winch everything ought to inspire that is 

 not a result of observation or of calculation." 



