554 GEOFFREY SMITH. 
of morphologists, and perhaps still is, to imagine that a primi- 
tive ancestral form must have been simpler and have 
exhibited less complication of structure than its modern 
representatives. In pursuance of this preconceived notion 
the simplest organised members of a phylum or smaller group 
of animals was always hit upon as representing the ancestral 
form ; but too often it has been shown that this simplicity is 
the result of secondary degeneration or simplification of 
structure. We have only to mention the Archianelida and 
the Marsupials to indicate what has been the trend of 
morphological opinion on this subject. 
It is often complained, especially by naturalists immersed 
in the positive details of what may appear more modern and 
fruitful branches of inquiry, that speculative morphology, 
as a reputable department of biology, is dead, killed by the 
wild speculations of its devotees. But it may have escaped 
their attention that the tendency of speculative morphology 
to-day is to display a more cautious temper than heretofore, 
and instead of attempting to link phyla with phyla by golden 
bridges of aérial speculation to undertake the more modest 
task of tracing the lines of descent within a smaller range 
of organisms, the history of whose evolution has been accom- 
plished at any rate somewhere within the period of time 
represented by the stratified rocks. 
If the family Anaspididz was already fully differentiated 
in the Carboniferous period and the family Nebaliidz in the 
Cambrian, it may well be conceded that to look for the 
ancestor of the Crustacea or to prove that Peripatus really 
links the Arthropoda and Annelida together are tasks which 
the cautious morphologist may well abjure. But that specu- 
lative morphology, when content to deal with the phylo- 
genetic history of fairly confined and homogeneous groups 
whose fossil ancestry have been preserved for us through a 
long period of time, is altogether idle we need not admit. 
And if a general consensus of opinion might at some future 
time be achieved, that the process of evolution in such groups 
has not been effected by the gradual complication of an 
