[3] CHROMATOPHAGUS PARASITICUS. 1129 



served in 1876 by I). Fouquet'* in trout fry in the fish-cultural tanks of 

 the College of France. For about ten years an epidemic was raging 

 among the young individuals of Tnitta fario L. contained in said tanks, 

 ''caused by the presence of infusoria," described in a treatise by Fou- 

 quet. It will be necessary to enter more fully into this investigation 

 which Fouquet made, under the direction of Balbiani, because many of 

 the phenomena described by him are closely analogous to those ob- 

 served by me, while on the other hand there are many points in Fou- 

 quet's treatise which can in no way be harmonized with my observa- 

 tions. 



The symptoms of the disease in the case observed by Fouquet doubt- 

 less agree with those described by Hilgendorfand Paulicki, as observed 

 by them in the Hamburg Aquarium, and those recently observed by 

 me. 



Fouquet likewise observed on the skin, fins, eyes, and gills very dis- 

 tinct round milk-white spots, having a diameter of from 0.3 to 0.8 

 millimeter. A microscopical examination showed that each spot had 

 been caused by the presence of a ciliated infusorian. While Hilgendorf 

 and Paulicki state distinctly that " the epithelium, without exhibiting 

 any other changes, forms a considerable protuberance over the para- 

 site," Fouquet^ has observed that " the skin is covered with a viscous 

 layer, and that the cells of the epithelium have changed." Sometimes 

 Fouquet lluds two or three infusoria of the same or dillerent size in the 

 same cyst, and states distinctly that the form of the young individuals 

 of these infusoria differs from that of the grown individuals. 



The former, he says, are " longer," and the latter " more globular." 

 The cuticle is. very elastic, transparent, tolerably tough, and covered 

 with very flue cilia, " presenting everywhere the same length, and run- 

 ning in lines which are twisted in spirals and cross each other." The 

 cortical layer [ectosarc] is pale, forms " a white band," and contains 

 scarcely visible trichocysts and numerous contractile vacuoles. The 

 endoplasm is granular and is not stained by carmine. It contains 

 ''blackish pigment spots of irregular shape," which, however, do not 

 occur in all cases. At the anterior pole Fouquet observed a small 

 round opening, measuring 0.04 millimeter in diameter, surrounded by 

 much larger and thicker cilia than are found on other parts of the sur- 

 face of the body, radiating from the i^eriphery toward the center. Be- 

 low this there is a small cavit}" terminating in a cul-de-sac, and formed 

 by a transparent membrane. Fouquet states further in a very em- 

 phatic manner that this orifice is not the mouth opening, but that it is 

 rather " a modified mouth, transformed into a sucking-disk." In proof 

 of this strange assertion, he states that he never found solid food inside 



■'D. Fouquet: " Note sur une espeee d'infusoires imrasites des poissons d'eau douce," in 

 Archives dc Zoologie expdvimeniale, published by Henri cle Lacaze-Duthiers, vol. v, 

 1876, p. 159. 



6 Fouquet, I, p. 34. 



