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The inter-relationships of the Ichthyopsida. 
A contribution to the morphology of Vertebrates. 
By J. Bearp, Marine Station, Dunbar, Scotland. 
Morphology has its traditional beliefs. Some conclusions are so 
obviously true, that to question their right to be considered as estab- 
lished tenets of the science is little short of heresy. 
Almost everybody believes them, because hardly anybody has had 
occasion to doubt them. 
It is so obvious, that, for instance, the lungs of higher Verte- 
brates are direct derivatives of the swim-bladder of fishes, that only 
two morphologists have been rash enough to express their dissension 
from the supposition. In a recent text-book, it is true, the lungs are 
on one page considered as probably having originated from gill-clefts, 
but a few sides further on the orthodox view is also approved. 
If the present arrangement of the fishes (including the Dipnoi) be 
accepted, the one view is just as good as the other. 
If the arrangement be accepted! — ,,Surely‘‘, some morphologist 
will say, „nothing stands on a better basis than the time-honoured 
grouping of the fishes. Not only does it accord so well with the facts 
of comparative anatomy, but it explains and illumines so many diffi- 
cult questions of embryology. Before all, the acquisition and loss of 
food-yolk, that stumbling block, in more ways than one, of the em- 
bryologist“. 
With an altered arrangement, what is to become of a recent 
ingenious, not to say romantic, essay on the gastrulation of the 
Vertebrata, an essay which so clearly depicts how simple the gastru- 
lation of this division of the animal kingdom becomes, as soon as the 
all-potent influence of the repeated loss and gain of food-yolk is ad- 
mitted ? 
There is no difficulty in admitting the influence of food-yolk per 
se, but too much depends on the assumption of its repeated loss and 
gain. 
The fact that some Vertebrates have eggs with much food-yolk 
and others eggs with little food-yolk is patent, but that fact in itself 
