38 MOLLUSCA. 
in the third, a syphon and no feet; in the fourth there is an 
abdominal syphon and no feet ; in the fifth there is a foot 
but no syphon; while, in the sixth, neither foot nor syphon 
can be discovered. In the formation of his genera, Poli takes 
advantage of the various forms of the cloak and the branchiz. 
To the celebrated Cuvier, the conchologist is also under 
the greatest obligations. By applying his vast knowledge 
of anatomy to the examination of the molluscous animals, he 
has unfolded many new conformations of parts, and exhi- 
bited many unlooked-for relations. The vast collection of 
objects, the spoils of all the museums of the continent, which 
Paris once possessed, lay open to his inspection, and his in- 
dustry appears to have been equal to the harvest which in- 
vited him to labour. 
In his first attempts to classify the molluscous animals, as 
contained in his Tableau Elémentaire de [ Histoire Naturelle 
des Animaux (1798); and his Legons d Anatomie Comparée, 
(1800-1805), he employed chiefly the characters which the 
preceding writers had developed, in his inferior divisions ; 
but in his primary distinctions, he distributed the mollusca 
into three classes: Cephalopoda, having the head covered 
with tentacula, serving as feet; Gastcropoda, with the head 
free, the animal crawling on the belly; and Acephala, hav- 
ing no distinct head. 
Some years after the appearance of this classification, 
Cuvier directed more of his attention to the internal struc- 
ture of the mollusca, and, by means of accurate dissections, 
obtained a more intimate acquaintance with the organs and 
functions of these animals than any of his predecessors had 
acquired. The information which he thus gained was com- 
municated to the public at different periods, in the well- 
known publication Annales du Museum d’ Histoire Nats- 
