AND THE LOWER ANIMALS. 13 



ing no apparent resemblance to that from which it 

 sprung. Then this animal begets, of itself alone, and 

 from all parts, a great number of other creatures, 

 which most frequently are unlike itself. Here several 

 individuals and several generations start from one and 

 the same germ. Moreover the differences are seen 

 not only in a single specimen examined at various 

 periods of its life, but among all the generations which 

 succeed it ; these invariably differing from one another 

 up to the last, which alone reproduces the primary 

 type. True to our metaphor, we may say that the 

 course pursued by Nature is at first single, and almost 

 direct, but that it soon divides and subdivides into 

 more or less tortuous paths, which lead invariably to 

 the same terminus. 



Although these facts are referrible to the same 

 cause, and to common fundamental principles ; 

 although they are in reality but a continuation of the 

 embryogenical phenomena, they are sufficiently dif- 

 ferent to admit of our distinguishing them by appro- 

 priate expressions. We shall see, moreover, that the 

 simpler forms are involved in the more complex 

 ones ; and unless we would add to the difficulties of 

 the subject, we must designate them by special 

 names. 



Consequently I shall term transformation, the series 

 of changes which every germ undergoes in reaching 

 the embryonic condition ; those which we observe in 

 every creature still within the egg; those, finally, 

 which the species born in ah imperfectly developed 

 state, present in the course of their external life. 



I shall retain the term metamorphosis for the alter- 

 ations undergone after exclusion from the egg, and 



