160 : Prof. M‘Tutosh’s: Notes from the 
with sufficient continuity to evolve anything more than.a 
variation. 
The differences in the various races of Félograna do not 
appear to be so great as to warrant specific separation, and 
this is the more noteworthy in a species so widely distributed 
and so plastic. ‘The variations lead to no change of habit 
or surroundings, no essential change in general structure, 
and the different methods of reproduction remain more or 
less the same throughout. No variety seems to excel the 
other in its influence on the stability of the species, or to 
lead to fixity and the formation of a new species, and the 
“extermination of the older and less improved forms.” 
This species does not conform to the view that the “lesser 
differeuces characteristic of varieties come to be augmented 
into the greater differences characteristic of species”’*. If 
the struggle for existence held in the ordinary way, it is 
reasonable to suppose that certain variations of structure 
and develappremt would have been singled out as permanent 
—to the exclusion of others. 
The differences between the varieties of Filograna are 
more pronounced, perhaps, than in such a case as A. G. 
Mayer’s lpenthesis folleata and Pseudoclytia pentata, the 
former with the typical four, and the latter with five radial 
canals, gonads, and manubrial lobes. The Ccelenterates, 
moreover, have a more simple structure, and their gelatinous 
tissues respond more easily to sudden variations. 
Whilst there is wide variability in the plastic branchia, 
eyes, opercula, the number of ‘‘ thoracic ”’ segments, and the 
absence or presence of buds, there seems to be more or less 
uniformity in the structure of the bristles and hooks as well 
as of the tubes from pole to pole of the world. It may well 
be asked why the environment has not altered these organs 
(bristles and hooks)? Their functions, it is true, aed not 
altered, but neither have the functions of branchiz or 
opercula. 
Yet, after all, and taking a broad view of the species, 
Filograna remains the same, and leads to no other type, for 
the Spirorbids, which have similar collar-bristles and 
branchie, are joined by no intermediate forms, their tubes 
are coiled and massive, and their opercula larger and 
caleareous. No change of surroundings in the varied 
waters stretching from Arctic to Antarctic seas makes the 
species other than Filograna. Moreover, there does not 
seem to be any correlation in the parts which vary, even the 
absence of the opercula and the presence of the enlargement 
of the tips of the branchial filaments are by no means 
* Darwin, ‘Animals and Plants under Domestication,’ vol. i. p. 7. 
