Trans. NN. Y. Ac. Sct. 54 Fan. 21,- 
rudimentary and imperfect organs of this sort. This is one of the 
many mysteries of the geological record, that the successive steps in 
the development of means of offence and defence should be so rarely 
found, and it is one of the difficulties of Darwinism as the theory o 
the universe. Incomplete organs of offence and defence would often 
be inoperative and useless, like a bridge which is of no value what- 
ever if it only partly crosses a stream. The horns of a bull can 
be of little service, till they project from the head and are well pro- 
gressed on the road to maturity. 
In geological history there is recorded a well-marked progress in 
the character and efficiency of the devices for offence and defence. 
Taking for example the placoderms of the Devonian for our starting- 
point, as these are the earliest well known fishes, we find them en- 
cased in armor which would bid defiance to all offensive weap- 
ons ; but it was so much of a load to carry that they must have been 
inactive and unenterprising animals. In the Carboniferous age the 
placoderms had given place to the scaled ganoids and sharks, which 
were less protected by armor but more active. These continued 
their reign till the middle of the Cretaceous, when the teliosts, like 
the trout and salmon, took possession of the waters. These-latter are 
but moderately provided with means of offence, and their thin 
and flexible scales afford little protection against attack; and yet 
they have practically taken possession of all rivers, lakes, and bays, 
and far outnumber other fishes in the open sea. By what means 
these small and light armed troops gained so complete a victory over 
their armor-clad predecessors, we can only conjecture ; but, it is prob- 
able, because they possessed greater intelligence and activity, their 
superior nerve-power being more than an equivalent for the passive 
protection of spines and bony plates. In the competition for the food 
supply which has apparently been the chief struggle of life, the quick- 
witted and quick-moving teliosts would circle around their slower 
rivals, and, by devouring their food, create a desert in which they 
starved. 
Similar facts may be observed in the history of the changing fash- 
ions in regard to offensive weapons and means of defence among 
animals, including Man. A large number of the Carboniferous sharks 
were provided with formidable spines; now only a few sharks and 
the chimeras retain their spines, but these greatly diminished in 
size, and more ornamental than useful. So, acentury ago, every 
gentleman wore a small sword, which he was only too ready to use. 
Where this fashion was general it became universal, for an unarmed 
man, in a crowd who carried arms, was quite at their mercy. 
In the middle ages all warriors were clad with mail; but this, to be 
