58 EVOLUTION AND THE 
a priori point of view. Such a process is, in fact, 
for living matter what Allotropism is for crystalline 
matter. And it so happens that the evidence in 
favour of the present occurrence of Heterogenesis 
is even stronger and much more varied than that 
in favour of the present occurrence of Archebiosis. 
Whilst the latter is a strongly warranted inference, 
the former is a matter of direct cbservation. So that 
concerning the present occurrence of Heterogenesis 
we may say, (1), that it follows as an almost neces- 
sary consequence from the physical doctrines of life ; 
(2), that it is a process which admits of daily obser- 
vation by skilled observers; and (3), that it explains 
many series of phenomena of the most varied nature, 
which would otherwise remain quite inexplicable.* 
* It is worthy of note, moreover, that it is the recognition of the 
present occurrence of Heterogenesis which is the : il-important neces- 
sity. A belief of this kind will carry with it all those important 
changes in biological doctrine and in medical science which seem to me 
both necessary and inevitable. The further belief as to the present 
occurrence of Archebiosis, is an extension of the ‘ Spontaneous Gene- 
ration’ doctrine, which, though it may be logically demanded and 
warranted, is one of altogether secondary importance ‘n relation to the 
changes of doctrine that it would involve. This state of things is the 
more important, because a belief in Heterogenesis is open to biologists 
of all shades of opinion. Indeed those biologists who still believe in the 
existence of a special ‘vital principle,’ would in all probability only 
ifner the occurrence of Heterogenesis from such experimental facts as 
would warrant, on the part of the Evolutionist, a belief in the present 
occurrence of Archebiosis. The Evolutionist, however, is bound to 
recognize a difference between living organic matter and dead organic 
matter, which the Vitalist, holding himself aloof from positive scientific 
