1877.] The Long-Jawed Goby. 477 
venes between the anterior margin of the orbit and the tip of the 
snout; in No. 2 it reaches to the posterior margin of the pre- 
operculum ; in No. 3 it ends level with the gill-opening; while 
in the largest individual it passes the origin of the pectoral and 
ventral fins. 
What can be the use of this long fold of skin and cartilage, 
which is not attached to the head except where it joins the 
mouth ; and which from its gradual development and ultimate 
large dimensions, must certainly serve some useful purpose ? 
Do not understand that I mean that every part of a creature is 
of use to it in its present mode of life, for as all naturalists know, 
there are in structural anatomy, just as in social life, cases of sur- 
vival ; remains of organs which were at some former time more 
developed, parallel in their nature to such survivals in costume, 
as the two buttons on the back of a man’s coat, once useful for the 
attachment of a sword-belt. But in this fish we have no case of 
survival, but one of unusual development; the family (Gobiide) 
to which it belongs presents no similar case, although its mem- 
bers have somewhat similar habits, and the conviction grows 
upon us, as we consider the subject, that the long jaws serve ' 
some useful purpose in the economy of the creature. In view of 
the half-terrestrial life led by this fish, I am inclined to suspect 
that the expansion of the upper jaw may serve for the retention 
of a small quantity of water, which, slowly trickling downward 
into the mouth and gills, keeps the latter moist when, from an 
unusually low tide or a dry season, the waters of its native 
creek fail, perhaps for several hours, to reach the holes in which 
the fishes dwell. It may be objected to this view that, were 
such an appendage necessary, or even useful, other species of 
Gobiidz, whose habits are similar, would show traces of a similar 
adaptation. This, however, by no means follows. Nature has 
many ways of working out the same end; and it must be re- 
membered that every real species when thoroughly known differs 
somewhat in habits from its congeners, or at least from its family 
friends. To take an illustration from the mammalia. The 
chimpanzee and the spider-monkey are both quadrumanous and 
both arboreal, yet the end which is attained in the former by its 
more perfect hands is reached in the latter by its prehensile tail. 
There are many fishes which can resist a tolerably long desic- 
cation, but the means by which they are enabled to do this vary 
greatly. The Ophiocephalide, a small family of fresh-water 
fishes found in the East Indies, have a cavity capable of contain- 
