Bibliographical Notices. 301 
weakest must succumb. Incipient structures being small, make but 
small demands upon nutrition, and may well therefore be indifferent. 
More advanced intermediate stages will make greater demands, and, 
being less perfect, will, in competition with more completely special- 
ized structures, be actually harmful. 
Nevertheless it may be admitted that whilst Mr. Darwin never 
professed to explain variability by the theory of natural selection, 
he may not have sufficiently recognized the universality of indiffe- 
rent variations. Heredity, towards the explanation of which Mr. 
Darwin merely threw out the hypothesis of pangenesis, would, of 
course, perpetuate these indifferent characters, as it does useful and 
harmful ones. On the Darwinian theory, the persistence of lowly 
organized types, of useless or even harmful structures, and of imper- 
fect adaptations, is perfectly explicable, as is also the existence of a 
variety of structures to serve one purpose, or conversely that of one 
organ serving divers purposes. These, together with the varied 
forms of Radiolaria or Foraminifera on which Mr. Mivart insists, 
are simply cases of the absence of a struggle or of its slowness in 
producing extermination. Such persistent forms as Nautilus and 
Lingula, to which Mr. Pascoe alludes, and to which we might pro- 
bably add the soft-bodied Peripatus and Amphiowus, are after all 
but few in proportion to the immense number of extinct species, and 
their existence is but a lingering one, “far from the madding 
crowd ;” and whilst no doubt, if looked at as worms, the two latter 
may be termed “ extremely specialized,” considered as Arthropods or 
Vertebrates they are certainly not so. 
These cases of persistence suggest what appears to be some answer 
to Mr. Mivart’s hypothesis, “ that specific differences may be deve- 
loped suddenly instead of gradually.” External conditions do not, 
as a rule, change rapidly. The rise and fall of land, changes in 
climate, or in the characters of aqueous sediments, are in the main 
gradual, A sudden variation will be of the nature of a monstrosity 
and but little likely to occur similarly and simultaneously in many 
individuals. The chances are also apparently against its being so 
well adapted to its surroundings as its slowly adapted congeners. 
The case adduced by Mr. Mivart of the change of Siredon into 
Amblystoma is not the origin of a new but the reversion to an old 
form ; and possibly the Ancon sheep would not have been perpetua- 
ted in a wild state. The latter is an illustration of the increased 
variability of forms when domesticated, a result that might well be 
anticipated from the unnatural suddenness of man’s changes in their 
surroundings inducing a condition of unstable physiological equi- 
librium. It was with reference to such views as to sudden changes 
that Mr. Darwin wrote, “Slight individual differences, however, 
suffice for the work, and are probably the sole differences which are 
effective in the production of new species.’ This sentence Mr, 
Pascoe apparently misunderstands as representing natural selection 
as the sole cause of the origin of new specics. 
It is in many cases difficult to gather how far Mr. Pascoe endorses 
Mr. Mivart’s objections, and space only permits a brief reference to 
