REPORT UPON A PARASITIC PROTOZOAN. 183 



Reproduction. — Former authors have described the multiplication of these para- 

 sites after leaving the host as taking place only in an encysted stage, but, as will be 

 seen below, I have found several variations in this multiplication which may serve as 

 connecting links between a simple division, as seen in other protozoa, and the repro- 

 duction as described by the authors mentioned above. In the case of one specimen, for 

 instance, which I liberated from the fish and then placed in a hanging drop, the move- 

 ments, which were at first very rapid and in all directions, gradually became slower 

 and the animal revolved in but one plana. At the end of about an hour, without form- 

 ing any cyst around itself, it divided and each half swam off independently of the 

 other, resuming the rapid motion. This observation demonstrates beyond a doubt 

 that Ichthyophthirius is capable of reproduction by division, without first becoming 

 encysted, which is, I believe, a matter of considerable importance from a practical 

 standpoint, for former authors have observed — and I have above confirmed their 

 statements in this regard — that it is not unusual to find several specimens of the 

 parasite in a single epithelial pustule or gallery, and this may occur even when infec- 

 tion is comparatively light. There are only two possible explanations for such an 

 occurrence. Either a multiple infection has taken place at the same point, or a single 

 infection has taken place and the parasite has grown and multiplied in situ. The 

 probabilities appear to me to favor the latter explanation, especially in view of the 

 above observation upon a specimen artificially liberated from the host. 



Fig. 3 represents a specimen which had escaped from a trout and come to rest at 

 the bottom of a glass jar at about 1 o'clock p.m. The animal was revolving very 

 slowly in different directions, so that the mouth was turned toward the observer at one 

 instant, in the opposite direction, or to the right or left the next instant. 



At 1:45 it had divided (fig. 4) into 2 cells, I and II. Each cell revolved inde- 

 pendently of the other, but they remained close together, although no surrounding 

 cyst membrane could be discovered. 



At 3:12 the cells had divided again (fig. 5), I giving rise to la and 16, II giving 

 rise to Ha and 116. No cyst was visible; cilia were present and the 4 cells were in 

 constant motion. 



At 4 p. m. (fig. 6) la had divided into la 1 and la"; 15 into lb' and lb" ; IJa into 

 lift' and 11a" \ lib into 116' and 116". By no test, either by direct or oblique light — 

 coloring methods could of course not be used — could I distinguish any cyst-membrane 

 around this 8-cell stage. Every cell continued to revolve slowly in its own area. 



At 5 p. in. the 16-cell stage (fig. 7) was reached. Ila' had given rise to Ila'i and 

 IIa' 2 ; Ila" to IW'i and IIa" 2 ; 11// to II&'j and II&' 2 ; lib" to llb'^ and llb" 2 ; la' to 

 la'i and la' 2 ; lb" to lb" x and I&" 2 . 



All of these divisions were observed directly and continuously. There can, there- 

 fore, be no doubt as to the origin of the various cells. The origin of the cells w, x, y, 

 and z } however, can be given with less certainty, although it is almost beyond question 

 that w arose from la" and x from 16' and it is probable that y arose from la", and 

 z from lb'. 



During the formation of this 16-cell stage a distinct surrounding membrane grad- 

 ually came into view, not, however, a common membrane inclosing all 1G cells in one 

 cavity, but a separate cyst for each group of 8 cells which had resulted from the two 

 cells I and II (of fig. 7) respectively, while between the two groups the membranes 



