HYPOTHESES OP VITAL DEVELOPMENT. 301 



forms yet undetected ; but the fact of this wonderful coin- 

 cidence of ascent in such large areas as Europe, North 

 America, and parts of South America, Asia, and Australia, 

 surely entitles the belief in a professional development of 

 life from lower to higher forms from thallogen to acrogen, 

 from acrogen to endogen, and from endogen to exogen;* 

 from invertebrate to vertebrate, from cold-blooded water- 

 breathers to warm-blooded air-breathers, and from simply 

 sentient existences to the higher activities of intellect and 

 reason. However complicated in detail, there can be no 

 gainsaying of this broad outline of ascent ; geologists may 

 differ in their interpretations of the means by which the 

 phenomena have been produced, but they cannot refuse as- 

 sent to the order in which they occur. Nor is it a mere 

 ascent in general terms from lower to higher classes, but 

 the orders, the genera, and the species partake of the same 

 progressional development this progression bearing a strik- 

 ing analogy to the order that prevails among the existing 

 grades of life, and in most instances also to the successive 

 stages of individual development. The forms, vegetable 

 and animal, of the Primary periods are on the whole lower, 

 more embryonic in aspect, and less specialised than the 

 forms of the Secondary, and these again less than those of 

 the Tertiary and Current epochs, t The ascent runs through 

 every ordinal group and section branching onwards and 

 upwards ; and is, we may rest assured, however little we 

 may perceive it, as operative now as during any of the by- 

 gone geological ages. 



* See Schemes of Vegetable and Animal Classification in Sketch No. 7. 



f " A progress from more generalised to more specialised structures " 

 (we quote Professor Owen, the most cautious, perhaps, of modern ana- 

 tomists), " analogous to that exemplified in the existing grades of animal 

 life and in successive phases of individual development, is appreciable 

 in the series of species which have succeeded one another upon our 

 planet." 



