THE LARGE CHINA-MARK. 325 



Along the back runs a dusky streak, and the surface 

 is covered with numerous little elevations, each of 

 which bears a single brown hair. It has only four- 

 teen feet, the abdominal prolegs being six in number ; 

 and this is the case in most of the caterpillars of 

 this tribe, although a few are as well furnished in 

 this respect as the caterpillars of the larger Moths 

 and Butterflies. When ready to change to the pupa 

 state, the caterpillar rolls up a leaf of the plant 

 which it inhabits, and spins a slight cocoon within 

 the little chamber thus formed, where it remains in 

 safety until the perfect insect is ready to emerge. 



Some of these caterpillars, however, are not con- 

 tented with forming a chamber in which to pass their 

 period of dormancy, but construct a small habitation 

 of one or more pieces of leaf, which they can drag 

 about after them by protruding the fore part of their 

 bodies from an opening left at the anterior end of the 

 case. One of the most remarkable of these is the 

 Pond- weed caterpillar, the larva of the Hydrocampa 

 Potamogata, or large China-mark Moth, which feeds 

 upon aquatic plants, and, like several other larvae of 

 this tribe, is capable of living beneath the surface of 

 the water. This caterpillar forms a little case of two 

 oval pieces of leaf joined together with silk at the 

 edges, and enclosed in this it crawls about, feeding 

 upon the leaves. When full-grown, however, it quits 

 this habitation, and cutting out another piece of leaf, 

 carries it to the lower surface of one of the leaves of the 

 pond- weed (Potamogeton natans), and fastens it there 

 so as to form a small chamber, from which the water 

 is expelled either by the direct agency of the larva, or 

 perhaps by the evolution of gas from the lower sur- 

 face of the leaf. To make this miniature water-bed 



