NO ABSOLUTE SPECIES EXISTS. 95 



to the sillcious sponges, and by thousands of microscopic 

 observations, by measurements, by drawings, by facts 

 and inferences, had produced evidence, which acute op- 

 ponents of the immutabihty 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 IMonograph.^^ 



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 



