1895.] Sponges: Recent and Fossil. 545 
independence, yet subject to a general subordination, so that, 
according to Haeckel and Schmidt, we are dealing neither 
with individuals nor colonies in the ordinary sense of the 
words.” He then quotes Schmidt as saying that “in place of 
an individual, or a colony, we find an organic mass, differ- 
entiated into organs, while the body, which feeds itself and 
propagates, is neither an individual nora colony.” It would 
thus appear that the long existence of the group has not tended 
to the fixation of characters, and it is probable that the ten- 
dency to variation now manifest, was just as marked in early 
geological time. 
The other point is of interest to evolutionists. Sollas points 
out that the same type of canal system exists in genera of 
three distinct and apparently unrelated families. Further, 
that the development of a cortex has taken place independ- 
ently, though on parallel lines, in several other distinct fam- 
ilies. Finally, that while calcareous and siliceous spicules 
have had an independent origin, yet the forms of the one are 
repeated by the forms of the other. He comes to the conclu- 
sion that variation does not depend upon accident, “ but on 
the operation of physical laws as mechanical in their action 
here as in the mineral world.” If, further, he continues, “ the 
independent evolution of similar structures is of such certain 
and quite common occurrence in the pany of the sponges, it is 
also to be looked for in other groups.” Thus, a multiple ori- 
gin of species, instead of being an improbability, is about as 
likely to occur as a single origin. Identically the same vari- 
ety could scarcely arise in two isolated localities, but forms 
now supposed to be genetically related, may have been of dis- 
tinct origin. 
