MOLLUSKS 
KE now come to another large and important group of ani- 
mals, with characters so peculiar to itself and differing so 
radically from those which distinguish any other class of living 
creatures, that it may be said to occupy almost a unique position 
in the animal kingdom. Recent investigations have demonstrated 
that the larval form of mollusks presents some remarkable 
points of similarity to the embryonic forms of the Annelida 
and to the larve of some other classes of lower organisms. 
This discovery is one of the triumphs of embryology in its patient 
search for that connecting-thread that weaves together all the 
varying forms of animal life. Aside from these subtle evidences 
of relationship revealed by the microscope, the mollusks appear 
to occupy a position of considerable isolation in the biological 
world. 
As accepted by zodlogists to-day, this phylum is but the rem- 
nant of its former self. Aristotle considered all creatures with 
a testaceous covering to belong to a single family, and those 
later patriarchs of biology, Linneus, Cuvier, and Lamarck, ex- 
tended the group to include the greater part of all the marine 
invertebrate animals. Little by little the phylum has been shorn 
of orders and classes. First, the worms and the Echinodermata 
were separated into distinct phyla; then the barnacles were dis- 
covered to be crustaceans, and were accordingly removed from 
their position as “ multivalves ” under the Mollusca ; then the 
tunicates, or ascidians, were found, through the critical examina- 
tion of their larval stage, to be merely masquerading as mollusks; 
and lastly, the brachiopods have been somewhat reluctantly re- 
moved from their old position with the mollusks and given the 
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