240 
BUI.LETIN OF THE BUREAU OF FISHERIES. 
It seems to be established that the supposed response of aquatic animals to atmos- 
pheric sounds of ordinary intensity is a myth, for sound waves propagated in air are 
almost totally reflected from the surface of water, but since sound vibrations are trans- 
mitted by water it does not follow that aquatic animals are necessarily deaf. An animal 
so abundantly supplied with tactile organs as a lobster has little need of ears, since sounds 
transmitted through the water would be perceived or felt by means of the sensory hairs. 
“The range of the average auditory organ in mammals,’’ to quote from the work of 
Prentiss, referred to above, “ is from 30 to 16,000 vibrations per second; waves of less 
than thirty vibrations per second do not usually produce auditory sensations, but are 
appreciable to the tactile sense. It is important to note that decapods respond most 
vigorously to low notes, and not at all to high notes or sounds produced by very rapid 
vibrations. This fact would seem to be good evidence that the vibrations imparted to 
the water and perceived by decapods correspond to those which produce tactile rather 
than auditory sensations in vertebrates.’’ It has been noticed that the so-called “audi- 
tory’’ hairs of certain crustaceans will vibrate to different musical notes, as will the hairs 
on the back of one’s hand or the strings of a violin, but they are not auditory, as 
Prentiss remarks. 
It is only natural to find that the senses of touch and hearing grade into each other, 
and in either case it is the effect of a vibration which is perceived. While it is a matter of 
convention how these sensations are described, it is evident that an aquatic animal like 
the lobster has no organ strictly comparable to a vertebrate ear or even to the auditory 
or chordotonal organ of insects, and that if possessed of such an instrument it would have 
little occasion to use it. The basal segments of the large antennae of Palinurus possess 
a peculiar structure often called a “ stridulating organ,’’ but nothing seems to be known 
of the real uses which it serves. (See p. 160.) 
To return for a moment to the sacs, which have the form of a narrow-necked bottle, 
and are carried in the antennulae, how do the sand grains find their way through their 
minute openings, guarded with hairs ? Professor Brooks has seen the megalops larva of the 
crab, Callinectes , pick up the grains and place them in the sac with its claws. As an 
illustration of animal instinct, this is truly remarkable, for it is peculiar to the larvae alone, 
the adult crab having no sand grains or otoliths of any kind in its sacs. The lobster at 
the fourth stage nearly corresponds to the crab megalops, but it has never been seen to 
behave in this manner. Whatever method the young may adopt to replenish their stock 
of sand after each molt, it is evident from the microscopical proportions of the grains 
that adults behave in a different manner. The animal in all probability thrusts its head 
in the sand, while the smaller grains, selected by the one opening of the “strainer,” grad- 
ally sift into the sac by the force of gravity. The spiny lobster {Palinurus) , which also 
keeps its antennal sacs well supplied with sand, has no claws with which to pick up any- 
thing, and must have recourse to a similar method. In reference to this peculiar need 
of the animal, it is interesting to notice that molting lobsters often burrow in the sand, 
where they remain for some time after casting the shell. 
