76 M. Hesse on a new Parasitic Crustacean. 
to be excessively caducous; for I have never found them adherent 
to the body of the Crustacean, but always beside it in its retreat. 
But as they are contained in an enclosure from which they 
cannot escape, there is the less inconvenience, in the interest of 
reproduction, in the fact that they detach themselves so readily 
from the body of the female. 
The male of this species is unknown. 
The embryo resembles that of all the suctorial Crustacea: its 
body is oval, with the forehead nearly square. The two sides 
are nearly parallel; and the posterior extremity terminates in a 
rounded point, presenting neither hairs nor terminal appendages. 
Of the three pairs of natatory feet with which the body is fur- 
nished, the first are simple, and the two others biramose, as in 
the species just mentioned; all are armed with long flexible 
setze destined to assist in natation. The articulations of these 
feet are very nodulose, and well fitted to facilitate movements. 
The buccal apparatus is proboscidiform and tolerably elongate ; 
it is widened at its orifice, aud appears to be furnished with two 
little jaws. It is erectile, and may lie along the thorax or rise 
up perpendicularly. 
The embryo, seen upon a white ground, appears black, but, 
when illuminated, it is red. It swims slowly, and with much 
less activity than those of the species with which we have com- 
pared it. 
Coloration.—This Crustacean varies much in colour. It is 
sometimes bright yellow slightly tinged with vermilion ; some- 
times it is of the latter colour but rather pale, brown, or leather- 
coloured (chamois). The head, the first thoracic segments, and 
the last segment of the abdomen are always white. The intes- 
tine, when full, is deep black; the ova are yellow or brown; 
the eye, as already stated, red changing to blue. 
Habitat. Found, pretty commonly, hidden beneath the scales 
of the young of the green-streaked Wrasse (Labrus Donovani*), 
where it lives as a parasite. 
§ 2. Mistory. 
It is already a long time since, while seeking for parasites on 
fishes, we first noticed that the young Green Wrasses often pre- 
sented on the fore part of the sides of the body, not far from 
the eye and the branchial aperture, a small tumour, the bright- 
red colour of which contrasted with the green tint of the fish. 
This peculiarity would not have attracted our attention so much 
if we had not seen it reproduced almost constantly under similar 
* The Breton fishermen call this fish Castrik. It is extraordinary that 
the parasite is absolutely found only upon this species, although there are 
several in the same genus which have the greatest analogy to each other. 
