MOLLUSCA. 3 



between the two leaves of the mantle, which are 

 covered with two separate shelly valves. They 

 live attached to other marine bodies. 

 VI. Tunicata or Tunicaries. 



Animal destitute of shell, but protected by an 

 elastic muscular mantle with two orifices. Gills in 

 the form of a net-work or of a riband stretched 

 across the internal cavity. 



Molluscous animals have sufficient maternal instinct 

 to select situations for oviposition most advantageous to 

 the development of their eggs. The Ampullariidce de- 

 posit their conglomerate egg-masses on stones and frag- 

 ments of wood in the shallow parts of ponds, where the 

 eggs are exposed to the full power of the sun. The 

 DoricUdiE and Limnwidw glue their ova together and 

 attach them in gelatinous bands to floating bodies, that 

 they may neither sink beyond the influence of the solar 

 heat, nor be dispersed by the action of the waves. The 

 lanthina and Argonauta bear theirs constantly about them, 

 the first attached to a vesicular float, the second con- 

 tained in a fraofile shell. The Carocolla conceals hers 

 under loose bark. The PytMce lay theirs under stones 

 and in holes of rotten wood. The Cyclostoma buries hers 

 in the yielding soil of decayed vegetable matter. The 

 thick-shelled Bulimia that live upon the ground, deposit 

 large oval calcareous eggs among the leaves, while those 

 lighter and more highly coloured species, that live upon 

 the trees, glue their coriaceous ova to the under surface 

 of the leaves, and some among them have sufficient in- 

 genuity to roll up the edges of the leaves, cement them 

 together, and form kinds of nests or cradles for their 

 tender progeny. 



