468 TRANSFORMATIONS OF iNSECTS. 
more elaborate and complicated than those of the full-grown 
males and females. 
The central figure represents a newly-born larva or Vauplius 
form; that on the left is of a Zoéa, after a moult, and the 
perfect female is shown upon the right hand side of the en- 
graving. 
These creatures may be found in the adult form upon the 
eyes, skins, and gills of many fish and Crustacea, and adhere by 
the matter which is formed upon the arched ends of the projec- 
tions in front of the straight part of the head, which is sur- 
mounted by two small antennae. The head, body, and abdomen 
are united, but there are constrictions which divide them to a 
THE METAMORPHOSES OF A Lernc@an ( Tracheliastes polycolpus). 
certain extent, and the intestinal canal may be noticed running 
down the midst. The female, at certain times of the year, has 
two long ovisacs at the end of the abdomen, for the reception 
of eggs which are developed within the body, but the limbs do 
not exist. The only exception to this statement is the arched 
structure ended by the sucker in front of the head, and probably 
this is formed by a pair of altered extremities. The Lern@a 
lives upon the juices of the fish, to which it adheres, and it pro- 
duces ova which in due time escape. 
The egg consists of an outer and inner membrane; and the 
embryo, which before hatching is more or less globular, is fur- 
nished with an eye and two pairs of oar-like legs, the second 
pair being subdivided, and all ended with bristle-shaped hairs. 
The embryo bursts forth, and a Mauplius or early larva, like 
that figured in the engraving, results. The legs are more fully 
