[9] CHROMATOPHAGUS PARASITICUS. 1135 



From the forej^oiiig- observatious upon the propagation of these infu- 

 soria the following conclusions may be drawn : In the first place, it 

 should be stated that propagation never takes place as long as the in- 

 fusoria are still lodged in the epidermis of the fish. After the infusoria 

 have reached a certain size by absorbing food, which consists princi- 

 pally of pigment cells, they leave the epidermis, swim about m the water 

 for some time, settle at the bottom, become encysted, and finally undergo 

 a process of fission, which, however, takes place only in the dark. In 

 about five hours this process of fission has been completed, and the 

 young infusoria leave the cyst. These young infusoria now seek the 

 epidermis of some fish in order to go through the same development 

 which we have observed and which we have endeavored to describe 

 above. Occasionally I found among the larger individuals on the skin 

 of the fish very small ones, which were exactly of the same size as 

 those which had just left the cyst. I have never been able to observe 

 any other process of propagation in the free-swimming individuals than 

 that by fission. 



In conclusion, I must add a few remarks as to the place in our zoolog- 

 ical system which will eventually be occupied by this infusorian. Judg- 

 ing from the phenomena observed by Fouquet in Ichtliyophthirius multi- 

 film and described above, I think that I am not in error when I express 

 the belief that the_ infusoria observed by me iu our aquariums belong to 

 the same species as those discovered by Fouquet in the tanks of the 

 College of France on the skin of Trutta fario L. My reasons for this 

 are: (1) on account of the agreement iu the mode of life of the two 

 forms; and (2) on account of the very striking similarity of their 

 structure and mode of propagation. There is, however, still a wide 

 gap between the Ichthyophthirius multijiliis Fouquet, and the infusorian 

 described by me, namely, the absence of an oral opening, the occurrence 

 of a sucking-disk, and the stable form of the body of the first- mentioned 

 species; and, on the other hand, the occurrence of a distinct oral open- 

 ing and the complete absence of a sucking-disk in the form observed • 

 by me, the mass of the body of which is, moreover, metabolic to a high 

 degree. 



Further investigations must show whether this supposition of mine 

 is well-founded, and whether Fouquet, when he says that his Ichthy- 

 ophthirius multijiliis has no oral opening, but a sucking-disk, has not 

 perhaps been the victim of an optical delusion. As has already been 

 stated, Saville Kent has likewise expressed a similar opinion grounded 

 upon physiological reasons. 



With the aid of all the literature on infusoria which was at my dis- 

 posal, especially Saville Kent's classical work, I have in vain endeav- 

 ored to find the position iu the system of the infusorian observed by me. 

 As to its structure it resembles most those infusoria which Saville Kent 

 places in the family of the Trachelocercidce^'' among the Ciliata-Holo- 



" Saville Kent, p. 509. 



