THE THRESHOLD OF EVOLUTION. 
145 
expressing the opinion that ‘ spontaneous generation undoubtedly 
played a more important part in the primeval period of the 
world’s history than at present/ frankly allows, notwithstanding 
his unflinching faith in the potentialities of matter, that ‘ we 
possess no certainty nor well-founded data on the point, and are 
ready to confess our ignorance. But, though as regards organic 
creation much may be doubtful, we may positively assert that 
it may have, and has, proceeded without the interference of 
external forces/ 
Now there is certainly nothing illogical in the opinion as 
thus stated, nor can it with fairness he looked upon as extreme 
even by the moderate Evolutionist. It is a simple avowal of the 
sufficiency of natural causes and conditions to account for the 
phenomena of life, when once established, and an outspoken 
warning that a rigid line of demarcation should always he drawn 
between that which admits of proof and that which at best can 
only be surmised.. 
Professor Virchow, another of Haeckel’s countrymen and his 
quondam teacher, one of the most accomplished biological writers 
this century has produced, has yet more emphatically declared 
that where the object of a speaker or writer is to instruct, ‘ no 
hypotheses or assumptions, however dogmatically insisted on, 
can stand in the place of details, the results of observation, 
experiment, and thought.’ It is, therefore, not surprising that 
Virchow should have vehemently attacked the Haeckelian system, 
or that two men with minds so antithetically constituted should 
thereupon have engaged in. a controversy almost without parallel 
for the acerbity with which it has been conducted. 
Let it not be imagined, however, that Haeckel makes any 
secret of his devotion to purely ‘ speculative science.’ In his 
reply to Virchow, entitled Freedom in Science and Teaching 
(1879, p. 63), he says: ‘In my opinion there is no boundary-line 
between the speculative departments of science and those that 
are actually conquered and firmly established ; on the contrary, 
all human knowledge is subjective.’ And in support of this 
proposition he then proceeds to show that even mathematics, 
which stands at the head of the exact sciences, is based entirely 
‘ on those deepest and simplest fundamental axioms which are 
incapable of proof. It will be seen presently to what extra- 
, vagant lengths ‘freedom in teaching’ may be carried where there 
i is a preconceived hypothesis to support. 
According to Haeckel, the Monera stand at the bottom of 
j his list of Protista , which are said to constitute a very natural 
i assemblage of organisms, presenting characters more or less 
common to animals and plants, but, in point of fact, comprising 
the Foraminifera , Amoebce, and Noctilucce, which are unquestion- 
' ably animals ; and the Diatomacece, ‘ Oscillarinece / and certain 
NEW SERIES, VOL. IV. NO. XIV. L 
