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-v^^alled 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 in 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 anah)gy 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 : — 



