466 
TRANSFORMATIONS OF INSECTS. 
have never attained that maturity which is observable in the 
Decapoda. 
The subdivision of the Crustacea called Entomostraca , the 
members of which have no branchiae, or any modification of other 
structures, for the purposes of respiration, the sessile eyes being 
generally united in one great mass, contains two orders. The first, 
the Copepoda, of which the genus Cyclops is well known, has the 
body divided into distinct rings, and has only a rudimentary 
carapace ; and the second, the Ostropoda, has a large shield-like 
carapace, as in the genus Cypris. All these minute Crustacea 
undergo metamorphosis, and they have been especially studied by 
Claus, and commented upon by Fritz Muller. 
The Copepoda (oar-footed) are very small, and the males and 
females differ, the latter carrying their eggs in a bag which hangs 
externally from the hind end of the body. These one-eyed 
creatures vary much amongst themselves, and have been classified 
under many genera. They occur in myriads, both in salt and 
fresh water ; and Cyclops quadricornis is perhaps the most abundant 
British species, and may be found in ponds and ditches in great 
multitudes. One genus ( Cetochilus ) supplies the whale with food ; 
and the Sapphirince are luminous at night in the South Sea. The 
Copepoda are born from the egg in the Nauplius form, and are 
totally unlike the adults. They have, at the earliest period, three 
pairs of limbs, which become eventually, and after metamorphosis, 
antennae and mandibles. A single eye, the labrum, and mouth, 
already occupy their permanent positions. The hind part of the 
body is usually short and destitute of limbs, and has two terminal 
setae or bristles, and the shape of the whole creature is very diverse 
in the different species. The changes which the first larval stages 
( Nauplii ) undergo during the progress of growth consist essentially 
in an extension of the body and the sprouting forth of new limbs. 
The following stage finds the Cyclops with a fourth pair of limbs, 
which are the future maxillae or jaws ; then follow at once three 
new pairs of limbs, the jaw feet and the two anterior pairs of 
swimming feet. The larva still continues like a Nauplius , as the three 
fore pairs of limbs represent rowing feet ; at the next moult, it is 
converted into the youngest cyclops-like state, when it resembles 
the adult animal in the structure of the antennae and mouth-pieces, 
