ON MOLLUSCA. 151 
Gmelin, who was too little of a zoologist to profit by the 
labours of the writers we have named, has scarcely made any 
change in this department, in his edition, the thirteenth, of 
the Systema Nature. 
An Italian physician, M. Poli, was the first | to establish the 
genera of mollusca, according to the animal alone, without 
paying any attention to the shell. In 1791 appeared the first 
volume of his magnificent work, on the testacea of the two 
Sicilies. It appears that he took into consideration all the 
molluscous animals, whether naked or testaceous, and divides 
them into three orders: 1. Mollusca brachiata, characterized 
by having several arms, in the manner of the hydra; 2. Mol- 
lusca reptantia, creeping after the manner of snails, by means 
of one broad foot, and always having a head and eyes; and 
3. Mollusca subsilientia, provided with a long foot, fixed to 
rocks, or not, and constantly devoid of head and eyes; this 
contains the bivalves and multivalves. 
During the ten or twelve years of the revolutionary whirl- 
wind which agitated Europe but few works appeared on this 
department of zoology ; indeed, it appears to have lain almost 
uncultivated, if we except some facts recorded in journals, and 
the establishment of some new genera. Thus the science re- 
mained stationary until, in 1798, our illustrious author, feeling 
like those we have before mentioned, that the methodical sub- 
division of the mollusca, like that of all other animals, should 
rest upon the study of organization, proposed his new classifi- 
cation. He thought in the first instance that the whole divi- 
sion of the malacozoaria should rise a degree in the animal 
series, and precede the entomozoaria, or animals articulated 
externally ; a second innovation’ was to unite definitively, as 
Pallas had done, under the classific name of mollusca, the 
molluscous worms of Linnzus, to his testaceous worms, that 
is, to consider the existence or absence of the shell, as but a 
very secondary consideration. He therefore made a distinct 
