114 THE WATER CABINET. 
pleasing spectacle of their increase, coming forth from 
the gelatinous mass in hundreds, like minute beads of 
gold, is lost without the aid of the cabinet in which to 
rear them. The young of most species of univalve 
mollusks are vagrant in their habits, and the jars in which 
spawn is hatched should be closely covered with perforated 
| card or gauze, fitting closely by means of India rubber 
rings. 
Since it is unnecessary in this work to give a classified 
history of the several creatures that may be kept in water- 
cabinets, I shall devote the remainder of the space at my 
command to notices of a few of the most attractive and 
best known species, and to a few hints on the general 
management of the cabinet. 
CHAPTER IV. 
LARVA. 
THE great class of insects comprises many remarkable 
and diverse forms, among the 560,000 species which Dr. 
Imhoff estimates to be now known to naturalists. Yet, 
various as they are, it is by no means impossible to define 
what are the distinctive features by which this class is 
separated from those which approach it in conformation 
and habits. A true insect has the body divided into 
three parts—the head, the thorax, and the abdomen. It 
has never more than six legs, and these are attached to 
the thorax. The segments of the body seldom exceed 
thirteen in number, one of which forms the head, three 
the thorax, and the remaining nine the abdomen. The 
