s 
110 Des Moulins on the genera Unio and Anodonta. 
mit of thé ladder whose descending steps degrade him to a frog; 
and by a further descefit even to a monad: by the other, he is 
placed on the lowest rung of the sublime ladder of created intel- 
ligences. But, let us speak to our senses: there is a point, in the 
hundred compartments of which I first spoke, where the homo 
sapiens finishes, a point where the brute begins; there is the 
impracticable leap, the gulf without a bridge, which separates 
the immaterial from the physical creation: there is the immense, 
the impenetrable abyss, which the hand of the Almighty has 
left between the Apollo and the frog. 
t may seem that these reflections are too high, or too abstruse 
if you will, to serve as the preamble to a critical examination of 
certain new species of shells. I do not think so, gentlemen; 
we can only judge piecemeal; and when the subject is intellec- 
tual, the pieces are principles. I thought a full explanation ne- 
cessary, that you might the better appreciate the elements of the 
discussion which I propose to submit to your consideration. 
From what I have stated, I now proceed to draw the single rule 
that will serve as the basis of my labors. 
Between the first and the last of our hundred compartments, 
there is a point where the man ends, where the brute begins; @ 
point at which, notwithstanding the imperceptible deterioration 
of external form, there is a change of nature, a change of mate- 
rial classification, a change of order, a change of class, a change 
of family, a change of genus, a change of species. ‘This consid- 
eration is enough for my purpose; without illustrations, its an- 
houncement is here sufficient. ; 
gentlemen, the most eminent zoologist now living in 
, (M. de Blainville,) stated twelve or fifteen years ago, 
that in considering the embarrassing variety of forms then known 
in the genera Unio and Anodonta, he felt the necessity of enqul- 
ring, whether, if the two genera* were joined again into one, as 
their comparative anatomy requires, that one should present ‘@ 
the classifying naturalist, an almost endless series of really dis- 
tinct species, or only one species infinitely variable in its forms. 
*In March, 1829, the translator expressed the opinion, “ that the seven genera, 
now referred to the family of Natades, are founded in artificial distinctions, aod 
not in nature ; and that in fact the family contains but one genus.’’—Trans. of the 
. Phil. Soc., Vol. 3, p. 398. 
