recommence its ciliary play, and appear in a still more advanced stage. It is still some months before it grows to its perfect form. One of these snails may deposit from two to three of these ova-sacs a week, producing in the course of six weeks or two months from 900 to 1,000 young,"
It is to the Microscope then we owe this pithy description of the progress ab ovo, of a species allied to the common IAmnaa of our rivers.
We now turn to the Sea-slugs, whose shell, where it exists, is small and thin, slightly rolled and pearly white, and partially concealed by the animal; in Bullæa (Bubble shell,) we find an organ resembling the gizzard of a fowl, paved with calcareous plates capable of crushing the shell-fish on which it feeds. Many specimens of this shell we have obtained on the shore at Geelong. The Pteropoda our readers are seldom likely to meet with;—the Lamp-shell (Waldheimia) is not uncommon, attached by its pedicel to the oysters from Western Port, and its structure is worthy of examination; it belongs to Cuvier's 4th class, Brachiopoda, commencing the bivalve section, the animals comprised in which take their name from the ciliated arms on the side of the mouth, wherewith their food is obtained.
The well known bivalve shells of the Oyster and the Cockle are good types of the Conchifera, the animals of which are, with few exceptions, aquatic, and range at all depths on almost every coast and every clime. There are amongst them some burrowing shells, as the large white oblong Anatina (Lantern shell?) such splendid specimens of which are found in Corio Bay, a species of Solen, or Razor shell, and the