Cellular Plants. 253 



ous details of vagrancy without jeopardy of the main chance. Such 

 change of habits might make a difference in various ways, including the 

 general morphology of such parts as the locomotive, absorptive and re- 

 productive. These are held in every mode of life subservient to the 

 question of sustenance. 



On the other hand, however, it is not necessary to admit that there 

 are not now to be found on earth conditions for living, almost precisely 

 like what might have been found in every age since the Silurian. We 

 have genera of Molluscoids and Crustaceans that have come down to us 

 with very little alteration from the earliest geological times. The Lin- 

 gula, a most conservative little Mollusk, who remains during life an- 

 chored by his stem to the bottom of the sea, has representatives buried 

 in the strata of every age from the Silurian up. While great changes 

 have taken place on earth, we are bound to perceive that there have al- 

 ways been tracts of sea water neither too hot nor too cold and furnished 

 with enough food to support the Lingula without requiring any great 

 change in the functions of his life. These spots have sometimes been 

 in one place and sometimes in another, and the wide distribution of the 

 animal has been effectual in always placing some of his tribe in an en- 

 vironment so congenial to his ancient hereditary habits as to require 

 little or no adaptive change in him. If one of his haunts was raised by 

 the slow oscillations of the earth's crust, and turned into dry land, its 

 very slowness gave him time to transfer his plantations into the deep 

 water. 



The small crustacean Ostracoids have likewise survived without much 

 change, and so have several others, and for the like reason, that there 

 has been a uniform submarine climate extending throughout the geol- 

 ogic ages, slowly shifting from one tract, or series of tracts, to another, 

 and transferring its animal and vegetable life with it. 



While this view shows how it is possible that a conservative type 

 might be perpetuated indefinitely with little change, it also shows that 

 substantially the same conditions which may be supposed to have been 

 necessary to originate organic forms in the first place, have never 

 ceased to exist, and are to be found on earth to-day. There appears no 

 reason why the process of the development of organic life from the min- 

 eral kingdom may not be going on to-day. 



On many accounts the present must be fully as favorable for the de- 

 velopment of animal life from vegetable as any preceding age. Vege- 

 tables exist in great abundance, and in greater variety and higher de- 

 velopment than ever before. I have shown elsewhere how vegetable 

 protoplasm might become separated from its natural resources of food 

 supply in its native vegetable, and by receiving its supply from foreign 

 sources become an animal or a parasitic fungus. The opportunities for 



