20 E. 8. Morse—Classification of Mollusca 
It is not enough to call them soft bodied animals; for in consid- 
ering their shell as a part of their organization, we have among 
them many of the hardest animals known, and we also have an 
number of soft bodied animals in the other branches. 
Their bilaterality, as cieiing anything definite, is an equally 
unsatisfactory character. Prof. Huxley has given an archetype, 
or common plan of the Mollusca, as he conceives it, with many 
rte a in the article ‘‘ Mollusca,” English Cyclope- 
dia, vi . 855. In his figure of the archetype, however, 
which i is sbalaterady peermedia we have details of structure 
= Sek Agassiz in his “ Methods of Study in Natural History ” 
also suggests his idea of the plan, or structure, when he says, p. 
34, “Right and left, have the preponderance over the other 
diameters of the body, ” and says furthermore, that collectors 
unconsciously recognize this in the arrangement of their collec- 
tions. “They instinctively give them the position best calcu- 
lated Hs son their distinctive characteristics, — to accomplish 
e them in such a manner as to show 
so obtains among ‘the Lamellibranchs. All Brachiopods are 
displayed from the dorsal or ventral valve. Also the Gastero- 
4 particularly the flat forms like Patella, Chiton, etc., and 
e Nudibranchs as well, while in the i of the nake 
Sdiapse we most usually bate s a dorsal vi 
Though Prof. Agassiz speaks of ie regs i - characterizing 
the Radiates, and similarly of articulation and vertebration as 
characterizing the Articulates and Vertebrates, yet Mollusks are 
spoken of as first introducing the character ‘of bilaterality, or 
division of parts along a longitudinal axis, that prevails through- 
out the Animal Kingdom, with the exception of the Radiates, 
This then can be no restricted definition for the Mollusca, since 
it pervades the two higher branches; and who will deny the 
evidence of bilaterality among the Radiates, the higher Hchino- 
derms for instance, as Clypeastroids and Spatangoids, where we 
have as good a definition of a longitudinal axis as we obtain in 
many Mollusks. Even among the Polyps, as in the Actinaria, 
the antero- — axis is eepaeed expressed in the undue prom- 
inence of the primary rad. 
Prof. Dana se been the first to publicly announce the plan 
of Mollusca, when he says, “The structure essentially a soft, 
fleshy bag, containing the stomach and viscera, without a radiate 
structure, and without articulations,’ 
* Dana’s Manual of Geology, p. 148. 
* 
