in the Animal Kingdom. 141 



It has thus been shewn, 



Istly, That a heterogeneous or special structure, arises only 

 out of one more homogeneous or general, and this by a gra- 

 dual change. 



2dly 9 That the manner of the change, is probably the same 

 throughout the animal kingdom, however much 



3<%, The direction (or type) and degree of development may 

 differ, and thus produce variety in structure ; which however, 

 there is good reason to believe, is 



4tthly 9 In essential character, fundamentally the same. 



5th?y, That no two individuals can have precisely the same 

 innate susceptibilities of structure, or plastic properties; and 

 therefore, 



6thly, That though all the individuals of a species, may take, 

 in their development, the same general direction, there is a par- 

 ticular direction in development, proper to each individual. 



Ithly, That structures common to a whole Class must, in a 

 modified form, re-appear in individual development; and, 



Lastly, That they can re-appear in a certain order only ; viz. 

 in the order of their generality in the animal kingdom. 



It lias been our endeavour, throughout this paper, to limit 

 the idea of fundamental unity of structure, to essential character 

 alone; specific, and even individual peculiarities, however in- 

 appreciable, forbidding more. Each germ, even when pre- 

 senting the merely animal type, must do so in a modified and 

 peculiar form ; on which the nature of its future metamorphoses 

 depends : and if in the course of embryonal life, there occur re- 

 semblances in certain parts of structure, to corresponding parts 

 in other animals, they are no more than resemblances ; since in- 

 dividualities cannot be laid aside. 



There is a danger in the present day, of generalizing too free- 

 ly ;* of carrying transcendental speculation much too far ; of 

 being so captivated by " the idea of a subjective unity, that real 

 variety may be lost sight of ; as bright sunbeams veil myriads 

 of worlds, that might shew to mortal man, what they are, com- 

 pared with his world, and how little he is in the latter." ( 



* See an excellent chapter on the " Unity of Design" by Dr Roget : Bridge- 

 water Treatise ; vol. ii. p. 625. 



t Valentin, Fragmente zu einer Kunftigen Gesetzlehre der individuellen 

 Entwickelung, in his Entwickelungsgeschichte, &c. S. 566, 



