192 The American Naturalist. [March, 



which most of these forms are destitute. The same was prob- 

 ably the case with the period which we now have under review, 

 and of whose life we find few forms except those which habit- 

 ually dwelt upon the bottom. The ocean may have been as full 

 of life then as it is to-day, many of the swimmers of that 

 period, perhaps, representing the ancestral lines out of which 

 the bottom dwellers had evolved, and which are still in a 

 measure preserved for us in modern embryos. These primeval 

 forms may have been even less suitable for fossilization than 

 their counterparts of to-day. The diatoms, the radiolarians, 

 and other minute existing forms have silicious shells capable 

 of preservation. It is quite possible that the early protozoa 

 and protophytes had no such skeletal parts, and that when 

 they died all trace of them departed. 



How far back, then, from the earliest age of fossils must we 

 place the actual date of the origin of life ? Ages perhaps — 

 epochs — a period as remote from the Cambrian in one direct- 

 ion as we are in the opposite. It may have taken as long, or 

 longer, to develop the trilobite as it since has taken to develop 

 man. During the whole of the immensely long period in 

 which the miles of earlier strata were being deposited, the 

 ocean may have been the seat of an abundant life of the lowest 

 type, and this a very slowly evolving one, the conditions being 

 such that competition and the struggle for existence were not 



Of the forms of life now existing, the most abundant and 

 the lowest in organization known to us are the bacteria or 

 microbes — omnivorous life specks, feeding alike on animals 

 and plants, and fairly assignable to neither. Possibly life had 

 its origin in forms like these, or in still lower stages of protoplas- 

 mic activity, and from this condition developed, after an inter- 

 minable period, into the simple oceanic protozoa and proto- 

 phytes typified by the radiolorians and the diatoms, the lowest 

 forms having characters common to both animals and plants, 

 while their descendants divided definitely into plants and 

 animals. 



The period here referred to, and -that subsequently consumed 

 in the development of the trilobite and its companion forms, 



