270 The American Naturalist. [Mareb, 
In general, the Noctiluca responds more readily to stimuli at night 
than in the day-time, and this is true even under artificial conditions, 
For instance, the record of one set of animals kept in the light from 
the beginning to the end of the experiment, and that of another kept 
in the dark is almost identical. M. Massart is inclined to attribute this 
regular variation of sensitiveness to memory on the part of the animal 
rather than to the influence of light, and his experiments would appear 
to prove his theory. 
That the irritability of the Noctiluca varies with the temperature 
and density of the water is demonstrated in a few carefully conducted 
experiments, the results of which are given in tabulated form. Inci- 
dentally, M. Massart observed that the normal specific gravity of the 
the Noctiluca is 1.014, but that this is increased or lessened with the 
varying density of the water. 
In conclusion, the author calls attention to the analogy between the 
irritability of the Mimosa pudica and that of the Noctiluca, the one 
manifesting itself in movement, the other by the emission of light. 
(Bull. Sci. de la France et de la Belgique, T. XXV, ler Partie, 1893.) 
The Production of Sound Among the Ants.—That ants 
have some means of communicating with each other is well-established. 
The experiments of Landois and those of Lubbock suggest that this 
communication is carried on by means of sounds produced and heard 
by these small creatures, but which the human ear is incapable of 
appreciating. The observations of M. C. Janet, published in Ann. En- 
tomol. de France (Vol. LXII, p. 159) show that certain species of the 
Formicidae, notably Myrmica rubra L. and Tetramorium cæspitum L., 
are in the habit of making a stridulating noise, probably by reciprocally 
rubbing superficial parts of the body. A demonstration of this fact 1$ 
very simple. Ona small pane of glass put a ring of soft putty, and 
after carefully dropping in the middle of the ring, by means of a fun- 
nel, a mass of ants freed from bits of earth or vegetable matter, quickly 
cover them with a second pane of glass and press it down until there 
is just barely room between the two pieces of glass for the ants to move. 
If provision has been made for renewal of air the imprisoned ants will 
live for several days. On holding this little box of ants to the ear and 
listening attentively, a murmur is heard very similar to that made ih 
a liquid boiling gently in a closed vessel, and before long distinct 
stridulations can be heard in the midst of the murmuring. These 
sounds are heard only when the ants are disturbed. 
