THE NAUTILUS. 143 
ious colonies fixed forms; that is, will generation after genera- 
tion yield the same mode in measurements, or will changes in 
the local environment from season to season affect the develop- 
ing organisms to such an extent as to produce an unending 
series of slight variations? These were the problems that called 
for a solution. The hope of throwing some light upon these 
questions prompted the breeding experiments which were started 
in 1912.’’ 
Colonies of 200 each of two species from Andros, Cerion casa- 
dlance and C. viaregis Bartsch were originally introduced on 
certain of the Florida Keys. In 1915, 800 C. crassilabris from 
Porto Rico, and in 1916, 8,317 C. wa from Curacao were 
planted on Loggerhead Key. The shells were marked by filing. 
Some of these colonies have now produced a second generation 
of Florida-grown offspring. The present paper contains records 
of the results. In the case of C. viaregis Dr. Bartsch finds that 
the variations in the first and second generations are entirely 
within the range of the species in its original locality; the 
changed environment ‘‘ has not affected them in such a way as 
to produce such differences as one observes between the various 
colonies in the Bahamas.’’ C. casablancae gives practically the 
same result. The same holds with the first Florida generation 
of C. crassilabris. 
On Newfound Harbor Khy C. waregis has hybridized with 
the native C. incanum. The offspring show a remarkable range 
of variation; forms near typical C. incanwm and typical viaregis, 
all intermediates between these, but also forms closely resem- 
bling the mottled C. martensi group of the Bahamas. A state 
of flux has been produced by cross-breeding. The experiments 
indicate also an unusual fertility, and the suggestion is made 
that ‘‘ crossing has an energizing effect which seems to enable 
the new product to surpass its associated congeneric forms in 
the production of offspring.’’ 
Dr. Bartsch suggests that during the glacial period, when the 
low state of water united the numerous Bahaman Keys, ex- 
tensive crossing took place, this resulting in the efflorescence of 
new forms which we find to-day. 
A valuable section treats of the soft anatomy, which shows 
