78 M. Hesse on a new Parasitic Crustacean. 
and evidently the result of an erosion produced by the parasite 
in obtaining its nourishment. 
All these arrangements having been minutely described, it 
only remains for us to seek to explain their purpose. 
When the double-walled scales are extracted from the place 
they occupied, and examined on their flat side, the parasite 
which is enclosed in the cavity existing between the two surfaces 
may be seen through the aperture pierced in the upper part. 
Generally it only presents the anterior part of the body at this 
orifice, and it is difficult to extract it therefrom, seeing that it 
is retained by a purulent and agglutinative secretion, in the 
midst of which it is immersed, and which causes it to slip when 
we endeavour to seize it. This must be done with care, as the 
least rough contact may wound it and immediately provoke the 
emission of the substances contained in the intestine. 
The ova, which are glued together and form small, square, 
flat masses, also float in the above liquid. 
When taken out of its refuge, the movements of the creature 
are quick and repeated, but always the same; they are reduced 
to contractions in a vertical direction and to nutations of the 
head, which is agitated horizontally to the right and left, so as 
to give rise to a certain very limited reptation, which sufficiently 
indicates that it is destined only to furnish the animal with a 
means of changing its position, but not its place. 
The largest of the apertures, which corresponds directly, as has 
been stated, with the erosion or sinus produced below, leaves no 
doubt as to its nature or the purpose which has produced it ; it 
is evident that it is by this orifice that our parasite, finding itself 
in contact with the fish on which it lives, obtains from it its 
nourishment. 
As to the inferior aperture, it seems to us to be destined, by 
establishing a current, to facilitate the evacuation of the excre- 
mentitious matters which might accumulate im this retreat, and 
to renew the water, which, in consequence of the secretions, 
might be altered and no longer fit for respiration. 
The small apertures pierced in the upper wall are probably 
intended to correspond with the perforation produced at the 
apex of the cone formed by the accumulation of the scales, and, 
by admitting the external water, to facilitate also either the ex- 
pulsion and dissemination of the embryos, or the access of the 
male, which, concluding from the analogy of what is known to 
us, must possess means of locomotion which have been denied 
to his female. 
Lastly, as regards the retreat in which this parasite shelters 
itself, we shall content ourselves with the following supposi- 
tions :— 
