20 
THE GEOLOGIST. 
its false riba, to expand a fan-like membrane, by which it can ... for a little 
time sustain itself in the air. . . . The bones of this most interesting reptile 
are hollow and thin, but strong, without Haversian tubes, and having nu- 
merous lacunae ; the canaliculi are tine for a reptile, but partake in other 
respects of the reptilian characters. . . . The gannet, being peculiarly cha- 
racterized by the length of its wing-bones, is a very appropriate bird to 
compare both with the bats and the Pterodactyles ; ... the humerus, 
radius, and ulna partake of the (microscopic) characters observed in all 
birds whose wings are long and pointed. In the humerus vertical section 
(fig. 17) the Haversian tubes do not reticulate, but run nearly ]3arallel. and 
ultimatelv converging to a point, from which extends another tube, which 
converges in a similar manner. ... In the transverse section the Haversian 
tubes appear as round dots, the lacunae as small irregular specks, and the 
canaliculi beautifully reticulate, etc. . . . Furcula, fig. 18, coracoid, fig. 19, 
femur, fig. 20 ; transverse section, fig. 21 ; tibia, fig. 22, rib, fig. 21 ; furcula 
of swift, fig. 6. . . . The structure of the gannet ... in the principal bones 
admirably exhibits the beautiful adaptation of the microscopic structure of 
bone to the movements, habits, and well-being of the creature ; and in no 
bone is that adaptation more closely shown than in the coracoid — the cir- 
cular reticulations of the Haversian canals in which bone are assuredly 
designed to enable it to sustain the shock it must receive when the bird 
impinges on the water. ... 
" For ordinar}' purposes, the gelatinous homogeneous bones of fishes seem 
sufficiently strong for their mode of living, but a much more elaborate 
structure is requisite in the higher vertebrata. ... In the Ichthyosaurus 
and Plesiosaurus, the canalicidi, tliough finer than tliose of some other 
saurians, are few in number ; hence their bones are perfectly distinct from 
those of mammifers or birds." 
Mr. Denois then passes on to the more direct consideration of the 
structure of birds' bones : — 
" Comparisons," he says, " with the same bones in birds of similar flight 
and configuration of tbe wing are hiulily useful in elucidating this subject. 
Take, for instance, such birds as the ring-dotterel ; turnstone, dunlin, 
pigmy curlew, little stint, and other birds of that description, whose mode 
of flight is so similar that . . . the most practised sportsman ' cannot ' dis- 
tinguish one from the other by its flight. If we examine a portion of the 
ulna taken from the same part of tbe bone in any one or all of these birds, 
v. e shall at once observe a similar and singular correspondence in the dis- 
position of the Haversian tubes. Examine next the ulna of the greensand 
piper, a bird whose wing is broader . . . and not so pointed, . . . and 
whose flight is easily recognized from its congeners, . . , and there is ' an 
entirely different arrangement of the Haversian tubes, which are reticulated 
in every direction, while in the rest they observe longitudinal directions." 
AVhat conclusion can vre arrive at, Mr. Henrn's asks, but that these 
tubes are arranged in accordance with the Plight of birds ? and in 
confirmation of this view he points out that tlie starling, raven, jay, 
etc., in which the secondary quills are well developed, have all fine 
and numerous reticulated tubes : — 
" In the fowl they are very powerful, and the ulna contains numerous 
and fine tubes ; in the owls the same ; iti the hawks the Haversian tubes are 
large and much reticidated, and are easily recognized from those of other 
