28o 
FASCICULI MALAY BIASES 
is watched when it is hanging from the surface him, it will be remarked that 
the boat is constantly expanding and contracting, owing to the respiratory 
movements of the mouth, and that, although the movements are too gentle to 
overcome the friction produced by the body and tail, which hang more or less 
vertically downwards in the water, and so to cause the animal to progress in 
one direction or another, they produce distinct currents on the surface, which 
bring towards the mouth any minute particle which may chance to be floating 
in its vicinity. Every now and then, without apparent cause, the tadpole sinks, 
and lies resting on the bottom for some little time before re-ascending to the 
surface. Photographs, which 1 was so fortunate as to obtain, show that the 
surface film is perceptibly raised over the whole area of the float, owing to 
upward pressure of the body, and when the tadpole sinks a regular vortex 
is caused, down which floating particles are hurried. At the moment of sinking 
the animal permits the funnel to fold itself, indeed, it is this action which causes 
it to sink, and it is quite conceivable that some of these particles may be 
enclosed in the folded funnel and so conveyed to the mouth ; a glance at Fig. i 
will show how diflicult it would be for them to escape, were they once properly 
engulfed. 
The function of the horny teeth is a diflicult question, for their divergence 
in structure from the type apparently normal in frogs and toads shows clearly 
that they are not mere vestigial structures. Dr. Gadow' suggests that they 
are used for rasping the under surface of the leaves of water plants, but I am 
obliged to disagree with this suggestion for the following reasons : — (i) The 
habitat of the tadpoles is not one suitable for the growth of water plants ; (2) 
I have never seen the funnel unfolded completely except when it was in 
contact with the surface film, and, although the under surface of floating 
leaves might well take the place of the surface film, I do not think that the 
muscles would permit a rasping action, for which the plain conical teeth would 
be far less efficacious than if they were serrated in the typical manner, and (3) 
the food of the species, judging from the contents of the alimentary canal in 
several specimens, does not consist of rasped leaves. I cannot offer any observa- 
tions on the exact function of the structures, but I would suggest that one or 
more of three functions are possible : — (i) They may serve to strengthen the 
funnel when it is in use as a float, (2) they may increase its surface area 
and so make it more powerful, or (3) they may serve as additional 
factors in the retention of nutritious particles within the funnel, and in 
preventing the entry of harmful organisms or substances. 
It only remains for me to express my thanks to Professor J. Cossar Ewart 
for the use of his laboratory in working at the material upon which this paper 
is mainly based. 
I . Loc. cit. 
