1889 - 90 .] Mr W. L. Calderwood on Dactylopterus volitans. 137 
rapidly to the surface. Dactylopterus is, I believe, an example of a 
fish which can readily adapt itself either to a bottom life or to a 
more than pelagic one. It has a number of the gurnard characteristics, 
the free fin rays, soft and projecting downwards, the flattened head 
and ventrally protruding mouth, the heavy-looking rounded body. 
I am totally ignorant of any animals which prey upon Dactylopterus, 
but let us suppose that for some reason or other it becomes necessary 
for it to leave the bottom and take to the air, then the sudden 
expansion of bladder seen in the gurnard is prevented by the action 
of the strong bladder muscles. In addition to this, its air cavity 
has the highest possible dorsal position, as has been already shown, 
which must be of great service in enabling the fish to keep its 
somewhat unwieldy body in its natural position. The thin-walled 
secondary portion of the bladder can, of course, not be expanded 
owing to its complete envelopment in bone. From a study of the 
young Dactylopterus, i.Q., the fish formerly known as Cephala- 
canthus, it is evident that only the adult forms can have the power 
of “flight.” The pectoral fins of young examples are quite in- 
significant as flying organs. 
The smallest specimen I examined was If inches. Here, the 
pectorals, when placed along the side, reached only to the level of 
the second dorsal fin ray. The swimming bladder was as in the 
adult. I was unable to determine the period at which the fish first 
ventured into the air, but gauging by the development of the pectoral 
fins, it may probably be when it has attained the length of about 
6 inches. 
In the skull the encephalic arch is the only one which requires our 
attention. A strong solution of caustic potash is necessary to 
loosen the bony sheath of the head so that the superficial plates may 
be removed. From the basioccipital the neural arch slopes for- 
wards, and is modified in a peculiar way, so as to make room for the 
secondary portion of the swimming bladder. The exoccipitals send 
processes backwards curving at an angle and enclosing this secondary 
portion, and the paroccipitals take their position immediately in 
front. The processes of the exoccipitals are attached to the dorsal 
superficial plate, and flatten out posteriorly under the inner suture of 
that plate. Each exoccipital, with its process, in this way forms 
the outer margin of the secondary portion of the bladder. The 
