268 
BRITISH ENTOMOSTRACA. 
former being the female and the latter the male ; and it 
was these two different species that he had observed, as 
he imagined, in the act of copulation. 
Tilesius and others have doubted whether the long 
filaments attached to the posterior extremity of the thorax 
were really ovaries. This is now clearly ascertained to 
be the fact. They contain a great number of eggs, which 
are round, and disposed in one single row, and even 
young females are found, as is the case with other Ento- 
mostraca, to possess external ovaries filled with eggs. 
The young, when first hatched, are very different in ap- 
pearance to the adult. In form they resemble closely the 
young of the Cyclopidae, and, like them, undergo a series 
of changes of skin, or moultings, before they assume the 
completely- developed form of the parent animal. 
This family contains four British genera — Caligus, 
Lepeoptheirus, Chalimus, and Trebius. 
1. Caligus. — Eourth pair of feet slender, of only one 
branch, and serving the animal for walking. A pair of 
small lunules or sucking-discs on the lower surface of the 
frontal plates. 
2. Lepeoptheirus. — Eourth pair of feet as in Caligus. 
Frontal plates destitute of the lunules or small sucking- 
discs. 
3. Chalimus. — Feet as in two preceding genera. 
Frontal plate provided with a long and slender appendage 
adapted for prehension, arising from the centre of its an- 
terior surface. 
4. Trebius. — Fourth pair of feet slender, and divided 
into two branches, adapted for swimming. No lunules 
or sucking-discs on frontal plates. 
