HARLY ONTOGENETIC PHENOMENA IN MAMMALS. 155 
Aufl., 1854, 8.22, Scomberesox Camperi hasan air-bladder, 
Scomberesox Rondeletii has none. In other families, 
Squamipennes, Tzenioidei, Siluroidei, Cyprinoides, Clupeide, 
etc., the same is noted. I hold this to be an argument for 
looking upon the air-bladder as an organ that is fairly on the 
way to become rudimentary. Certainly not as an organ that 
is yet very essential to the life of many Teleost fishes in 
their present environment. 
At the same time the fact of the existence of such a very 
great number of Teleost species is certainly no argument 
that the whole of their pedigree must necessarily lie in the 
aquatic medium.! 
I will not go so far as to say that all Teleostomes and 
Dipnoi have descended from terrestrial, air-breathing tetra- 
pods, because the material upon which to base a similar 
conclusion is by far too scanty ; but on the other hand I will 
not either for the same reason anathematise any naturalist 
who feels inclined to go as far as that. It should certainly 
be kept in view that the incipient aeropneustic conditions 
which ensued upon the adaptation of posterior gill-clefts to 
aerial respiration need not necessarily have been accom- 
panied by a terrestrial life. Still it will certainly have 
contributed to render further adaptations to a terrestrial or 
rather amphibious existence easier. 
I must, however, yet allude to one argument which goes 
parallel to that derived from the air-bladder and lung- 
arrangement. 
It is an osteological argument and calls our attention to 
the fact that the mutual relation of the ossifications on the 
skull and visceral arches of the 'eleostomes are to such a 
1 While correcting the proof of these pages Assheton’s ‘ Development. of 
Gymnarchus niloticus’ (the Budgett Memorial volume, 1908) comes into 
my hands, in which I find the possibility of similar inverse relations discussed 
on arguments derived not only from lung and air-bladder, but on further 
developmental details concerning the vascular system and the gills, brought 
together under ten heads (I.c., p. 407). Gymnarchus belonging to a primitive 
family of Malacopterygii, it is only natural that I should welcome support, 
obtained independently along a perfectly different chain of reasoning. 
