Nest-Building Fishes. 165 
nuptial lustre, shows remarkable activity in selecting a site 
for an edifice, and transporting the building material thither. 
Fragments of all kinds of plants, gathered often at a distance, 
are brought home in his mouth. These are arranged as a 
sort of a carpet, but as there is danger of the light materials 
being carried away by the current, they are weighted down 
by sand to keep them in their places. Having entwined them 
with his mouth to his complete satisfaction, he then glides 
gently over them on his belly, and glues them with the 
mucus that exudes from his pores. More solid materials, 
sometimes bits of wood, sometimes bits of straw, which he 
seizes with his mouth, are adjusted to the sides of the floor 
to constitute the walls. He is now very particular. Ifthe 
piece cannot be properly adjusted to his building, and he 
does not lose patience in his efforts to fit it in, he carries it 
to some distance from the nest and leaves it. After the side 
walls are erected, a roof of the same materials with the floor 
is laid over the chamber. Firmness is given to the whole 
structure by passing over it with his body, the light and 
useless particles being fanned away by the action of his fins 
and the vibratory movements of his tail. In carrying on his 
building operations care is taken to preserve a circular 
opening into the chamber, his head and a great part of his 
body being thrust therein, thus widening and consolidating 
it, and rendering it a fit receptacle for the female. When 
choosing material, the fish has been seen testing its specific 
gravity by letting it sink once or twice in the water, and if 
the descent was not rapid enough finally abandoning it. 
Of the exact method used by the fish in binding the nest 
together we are indebted to Prof. Ryder. The male fish 
spins from a pore or pores a compound thread, using his 
body to insinuate himself through the interstices through 
which he carries the thread. The thread is spun fitfully, 
not continuously. He will go round and round the nest per- 
haps a dozen times, when he will rest awhile and begin anew. 
Its shape is somewhat conical before completion. The 
