THE COURSE OF BIOLOGIC EVOLUTION. 27 



in the Cenozoic ; and you have doubtless frequently heard 

 astonishment expressed at the great perfection to which the 

 articulated type attained in the Trilobite, the molluscan type 

 in the Ammonite, the piscine type in the Ganoid, the reptilian 

 type in the Dinosaur, and the mammalian type in the masto- 

 don, the highest expressions of all of which belong to geologic 

 periods, and whose living representatives, with few excep- 

 tions, belong to the humbler forms of life. 



DEVELOPMENT IX PLAXTS. 



As a specialist only in the lower of the two great kingdoms 

 it is not my place to enter into details respecting the working 

 of these several laws in the animal kingdom, even if I were 

 competent to do so. My illustrations must therefore be chiefly 

 drawn from plants. 



It is well known that the three principal groups of modern 

 cryptogams, the ferns, Dycopodiaceae, and Equisetaceae, repre- 

 sent the degenerate descendants of a vegetation which formed 

 extensive forests in Carboniferous time, and Hugh Miller, Dr. 

 Lindley, and some more recent authors have used this fact in 

 the manner above referred to, as demonstrating that the life- 

 series of the globe is as likely to be a descending as an ascend- 

 ing one, and that development as a general principle is not 

 proved. Of course it is now well understood that natural se- 

 lection does not necessarily produce an ascending series, as for 

 example, in parasitic degeneration. But the principle which I 

 have formulated to-night of type degeneracy has been almost 

 entirely ignored, although it is alone able to explain the most 

 important facts that seem opposed to evolution in general. 

 The modern degenerate cryptogamic vegetation is one of those 

 facts and to it I must devote a few moments of explanation. 



