NO ABSOLUTE SPECIES EXISTS. 95 
to the silicious sponges, and by thousands of microscopic 
observations, by measurements, by drawings, by facts 
and inferences, had produced evidence, which acute op- 
ponents of the immutability of species had not brought 
forward before me, that in these sponges, species and 
genera, and consequently fixed systematic unities in 
general, had no existence. The other division of the 
same class, the calcareous sponges, had been treated 
with unrivalled mastery by Haeckel in his Monograph.” 
He was able not only to confirm my statements, but, 
owing to the smaller compass and the greater facility 
of observing the group selected for study, to advance 
with more sequence and continuity from the observation 
of details to the whole, to portray its morphology, 
physiology, and evolutionary history with the utmost 
completeness. He then challenged the obstructive 
party with the assertion that, according to subjective 
opinion, either one or 591 species of calcareous sponges 
might be accepted, but “that no absolute species exists, 
and that species and varieties cannot be sharply sepa- 
rated.” Whoever after these demonstrations cleaves to 
the phantom of species, without either proving that 
the facts have been falsely observed, or that they 
may be interpreted otherwise than in favour of the 
stability of species—whoever, as Agassiz has: recently 
done, ignoring any such researches, publicly asseverates 
that in no single case has the mutability of any species 
been exhibited,—scarcely preserves the right to partici- 
pate in the great controversy by which Natural Science 
is now perturbed. 
There is, however, as we have already mentioned, a 
second direction in which the mobility of “species ” must 
