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 Crtistacea 

 undergo metamorphosis, and they have been especially studied by 

 Claus, and commented upon by Fritz Miiller. 



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 Sapphirmcs are luminous at night in the South Sea. The 

 Copepoda are born from the Qg% in the Naiipliiis 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 

 setse or bristles, and the shape of the whole creature is very diverse 

 in the different species. The changes which the first larval stages 

 {Naicplii) 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. 



