Prof. Agassiz on the Origin of Species. 153 
mals, and, perhaps, cease to be so confident as they seem to be, that 
these differences are trustworthy indications of the variability of species, 
€ eggs move about, as Planule, for a short time, and then become at- 
tached, as Scyphostomes, and pass the winter in undergoing their Stro- 
h 
the largest number of the H ydroids, produce their Meduse brood in the 
few breed later, in the in the autumn; so that, 
standing the regularity of their periodical return, Acalephs may 
led, in some condition or other, uring the whole year. ‘ 
hen considering Individuality and Specific Differences, as manifest- 
- thing striking in the features which distinguish classes, it is the def- 
iMiteness of their structural peculiarities; and this definiteness goes 
a Mereasing, with new and additional qualifications, as we pass from 
__. Class characters to those which mark the orders, the families, the 
1. ay and the species, Granting, for the sake of argument, that 
uy oo beings living at a later period may have originated by a grad- 
change of those of earlier periods, one of the most characteristic fea- 
*s of all organized beings remains totally unexplained by the various 
SECOND SERIES, Vor, XXX, No. 68—JULY, 1 eagles 
