PRE-CARBONIFEROUS FLOOR OF THE MIDLANDS. 
131 
tend to vary so as to suit those environments, and be, 
“in so far, unfitted for the average habits proper to the 
species. But these undue specialisations are continually 
checked by gamogenesis.” Thus the individual differences 
which would, if agamogenesis were the only means of multi¬ 
plication available, be a bane, are by gamogenesis turned into 
a positive advantage. Any member of a class of organisms 
which had previously multiplied by agamogenesis would, if 
gamogenesis should become available to it, thereby get an 
advantage over its fellows and rise into higher society. Thus 
we can account for the fact that the gamogenetic act not only 
becomes more common as we rise in the organic scale, but 
also less incidental, and a more serious and regular part of 
the life-history of the species. We can trace it from its 
origin in what was a mere chance fusion of two individuals to 
the highly specialised form in which it occurs in the highest 
vertebrates. 
But there is more than this, I think. It is a common 
truth that in agamogenetic modes of multiplication more 
individuals are produced than by gamogenesis. Therefore, if 
the species maintains its ground, more individuals must die, 
proportionately, in the former case than in the latter. Those 
that die must have been less fitted for the average life of the 
species ; so also must their offspring be, if they produced any 
before death. But in gamogenesis, cross-fertilisation and to 
a less extent self-fertilisation neutralise that “fatal narrowness 
of adaption” which tends to arise, and, in so far, requires the 
production of fewer young to ensure the continuance of the 
species. This is another advantage of gamogenesis. 
Finally, we must not suppose that this theory will explain 
everything. We must be content if it gives an intelligible 
reason for the cardinal facts and most of the details, leaving 
the apparent exceptions to be cleared up by future research. 
THE PRE-CARBONIFEROUS FLOOR OF THE 
MIDLANDS. 
BY W. JEROME HARRISON, F.G.S. 
(Continued from page 104.) 
9 .—The Longmynd Hills and the Stiper Stones .—West of 
Church Stretton the Lower Cambrian rocks, striking north¬ 
east and south-west, occupy a breadth of six miles, rising in 
the Longmynd Hills to a height of 1,674 feet. They consist 
of grey, purple, or green grits, sandstones, slates, and con¬ 
glomerates, whose thickness, unless they are repeated by 
