724 THE AMERICAN NATURALIST. (VoL. XXXIII. 
The preceding facts as to distribution indicate that the fish 
does not pass by these several stations below the second cata- 
ract. It is, therefore, probable that the very considerable num- 
ber of fish, which were taken over a limited territory, only a 
few miles in extent, were not individuals who were migrating, 
but fish that were living the year round in this locality. They 
were, in the full sense of the terms, healthy normal fish, and 
seemed to frequent certain holes, where they could repeatedly 
be taken with a circular throw-net. The males are smaller than 
the females, and although they are much less numerous, are 
generally taken in company with one or more females. 
Aside from the lack of evidence as to Polypterus being a 
migratory fish that can be deduced from the facts of distribu- 
tion, the continuance of mature individuals at Mansourah for a 
period of three months cannot be explained on the migration 
hypothesis. But the principal fact bearing against the latter 
view is that the adult fish is so affected by salt water that a 
slight increase in salinity kills it. On June to, at Inanieh, 
a point four miles from Damietta, we came upon a number 
of dead Polypteri thrown up on the bank. The water was 
slightly brackish, and the fish evidently had been killed by some 
such particular cause. No other kinds of fish were found dead. 
The salt water, which had reached this point owing to the low 
Nile, continued to back up the river, until seven weeks later, 
August 2, it had reached Toela, some thirty miles from the 
sea. Being then stationed at Mansourah, a number of fish 
were brought in to us, which for the first time during our stay 
here were not fresh. Rigorous cross-questioning brought out 
the fact that they had been picked up dead upon the river 
bank at this town, Toela, which was now dependent on the 
canals for drinking water and irrigation, the Nile there being 
brackish. Several of the fish which had been killed by the salt 
water were heavily laden with eggs. 
The chief reasons, therefore, for believing that Polypterus is 
not a migratory fish are : (1) It is unrecorded, in any numbers, 
at points intermediate between Mansourah and the second cat- 
aract; (2) females remain at Mansourah for several months 
longer than the actual time required for spawning ; (3) the 
