GILL] LIFE HISTORIES OF TOADFISHES 425 
that bone. It has been stated that the eyes are favorably placed 
for discovering prey; we may add that if they were lateral the 
head could not bury itself very far into the sand without impeding 
the vision. It is also useful that the surface of the head is hori- 
zontal, because in this way it is likewise covered by the sand. If 
the opercles do not beat when the fish is surrounded by water, they 
close the branchial apertures still more effectually in the sand. Now 
at the place where the two apertures project behind the head, there 
forms immediately a little vortex of sand which is thrown up by 
the water; little by little the sand-grains are deposited around it 
and the hole is formed without a single grain stirring afterwards. 
At the bottom of the hole may be seen a constant rising and lower- 
ing of a whitish body which is none other than the upper end of 
the branchiostegal membrane. This end is soft, spongy and dis- 
coidal, and is attached to the scapula a little below the spine which 
is a posterior lengthening of the latter bone. It is solely from this 
point, or the upper angle of the branchial aperture, that the water 
finds an egress, because a doubling of the skin which prolongs pos- 
teriorly the border of the operculum permanently closes the aper- 
ture. In other fishes the branchiostegal membrane is often seen 
to project to a great extent below and also a little backwards 
beyond the border of the parts closing the branchial aperture, and 
in the latter place this membrane supplies that which the opercle 
lacks in closing the corresponding portion of the aperture. 
In Uranoscopus, on the other hand, the upper border of the 
branchiostegal membrane does not project outside the edge of the 
opercle, because the latter, as has been stated, is enlarged by a mem- 
branous portion. Cuvier and Valenciennes’ noted this peculiarity 
in the following words: “The borders of the opercular valve are 
enlarged by a portion of the skin which adds a large band to them.” 
This skin portion is thick and notched in the margin, and covers 
pretty well over the scapular region. Also the free margin of the 
opercle is furnished with a portion of the skin, but narrower than 
that of the opercle. It is easy to explain the utility of these dis- 
positions. The branchiostegal membrane is constantly agitated to 
throw out the water admitted by respiration. These movements 
would be impossible while the fish remained buried in the sand, if 
the opercles were not adapted in such a manner as to oppose the 
obstacle which the sand placed in their way. As a matter of fact, 
the opercles are somewhat hollowed, and thus permit the branch- 
iostegal membrane to move freely within. The membranous por- 
* Hist. Nat. d. Poissons, 111, p. 292. 
