590 Cuin PInG 
stand the unfavorable external medium. In proving this the writer had 
several grown larvae kept in fresh water, which pupated afterward without 
difficulty. 
Young larvae of the first and second instars, however, require salt water. 
None of the young larvae placed in a fresh-water aquarium for a period 
of three days survived, although food was provided. During the growing 
period the larva requires conditions near to the normal — that is, a range 
of percentages of salt in water, within which only a little osmosis takes 
place between the external and the internal medium. In solving the 
problem of that general range, four sets of experiments were performed. 
In Experiment I, the young larvae were able to live in the water having 
low percentages of salt, while the older ones thrived better in the water 
of higher salinity. In Experiment II, most of the larvae could live in 
the salinities ranging from 1 to 8 per cent. Certain chemical substances 
dissolved in tap water may have had some effect, to a certain extent, upon 
the larvae, yet the results are plain enough to indicate their adaptability 
within a fairly wide range of different strengths of salt in water. In 
Experiment III, those larvae living in water having a salinity of from 1 
to 9 per cent attained full growth and pupated, while those in a 
salinity of 10 per cent died one day afterward. The fact that 10-per-cent 
salinity is the maximal limit, beyond which no larva could live, is well 
shown in Experiment IV, even in the:case of comparatively mature larvae. 
It is difficult to rear larvae of the first and second instars in salt water 
prepared in the laboratory; but in the water collected from the pools 
it can be done easily, even through all the stages of a complete life 
cycle. This difference may be due to the foreign food used, such food 
being less nourishing to the young larvae than the natural. And it is 
also due — perhaps chiefly —to the enriching nitrogenous substances 
brought to the pools through animal pollution. Such substances are 
entirely lacking in the laboratory aquarium. But in spite of these 
complications, most of the larvae did live and attain maturity within a 
general range of salinity of from 1 to 9 per cent, as shown in the four 
experiments. 
Garrey (1904) says, “‘A dilution or concentration of the aquarium water 
always causes an equivalent in the blood of the invertebrates, and osmotic 
equilibrium between the ‘ external and internal media’ is established.” 
In the pools the salinity varies from time to time; rain often lowers it 
