198 THE NORTHERN MICROSCOPIST. 

body of a fish or newt, and rapidly germinate, as ate, f, g. The 
manner of cyclosis of the protoplasm in the tube of the thallus is 
seen at %. 
It must be pointed out that want of knowledge of the life-history 
of this lowly form was the entire secret of its production as a case 
of Heterogenesis. The facts observed were correct enough ; but 
the other links that made the chain of which they were only a 
part, were unknown to the observer; and this is a fruitful source 
of “ fact,” such as is constantly offered for a similar end. By such 
a method of enquiry and research, the potato disease might well 
have been taken as the “transmutation” of the protoplasm of the 
potato into its blight! Indeed, heterogenetically, this was a far 
better case, for here we have (living) protoplasm to get the fungus 
transmuted from. But in the other case only the proximate | 
elements of the protoplasm of the dead fly. As it is, however, both | 
Achlya and Peronospora are known to have definite histories, and 
to depend ultimately upon the production of what are the equiva- | 
lents of genetic processes. 
It would indeed, in the absence of accurate knowledge, be much 
more to the purpose to say that the mistletoe was the direct result 
of transmuted protoplasm from oak or apple tree that becomes its 
“host ;” for verily it lives by the living matter provided for it. 
But the Botanist knows that the mistletoe grows from a fertilised 
seed. Not knowing the history of the Achlya, it is easy for the 
believer in Heterogenesis to take a blind leap over Nature’s elabo- 
rate arrangements for its continuance and multiplication, and 
assume that it sprang, without a progenitor or a past, into direct 
existence from the protoplasm (?) of a dead fly ! 
This is not a new process of inference in the history of Biology. | 
There was a time when every process that could not be explained 
as it was, was explained as it ought to be. It was gravely affirmed 
that ducks grew on trees, and elaborate drawings of the process 
are still in existence. We all know how hasty inference could 
account for the coming of the flesh-fly in the carcase of the dead 
sheep, by transformation. But gradually the illusiveness of this 
method of inference has become apparent. Biology to-day is as 
rigid a science as Physics in some of its methods ; this precision 
has “laid” the ghost of Heterogenesis. Life-processes are no 
more capricious than processes of crystallisation. The laws of 
Biology are laws as much as those of Chemistry. The lowliest 
and minutest forms which we have studied have a known history 
repeated (subject to the secular processes of the Darwinian law) in 
| all their successors. ‘There is no sudden caprice ; and therefore 
Heterogenists are fain to congregate about the fringe of vital forms 
where our knowledge of life-history is not complete, and where 
the minutest forms are found. We never hear of either crustacean 
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