200 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



tliat each space corre.s])ouds to a primitive fiber bundle wliose normal 

 aspect is profoundly moditled by the presence between its fibrilltB of 

 elements of a i^arasitic nature, whence results a slight increase of width 

 of the fiber bundle. Most often the fibrillte do not present a sensible 

 alteration. Sometimes (probably when a great quantity of the para- 

 sitic element has led to a considerable separation) the elasticity of the 

 fibrilhie is overcome, rupture resulting. Even under these conditions, 

 however, the muscle stride remain exceedingly clear, no degeneration 

 ever having been observed, as in Calliomjmus and the barbel. 



The nuclei of the muscle fiber are more numerous and smaller than 

 normal; this feature is particularly well shown by safranin (Henneguy, 

 1888). 



Effects. — The muscular vigor is considerably diminished. Thus, if a 

 number of P. rectiro.strls living in the rivulets of the salt marshes be 

 frightened out of their shelter among the vegetation, even although 

 the new shelter sought by them be near at hand, the diseased white 

 individuals (immediately recognizable against the strongly contrasted 

 muddy rivulet bottom) lose ground and remain considerably behind the 

 sound ones. Further, one knows with what ease the prawns jump out 

 of the vase in which they are held captive. If sound and opaque 

 Ijrawns be placed together in a basin, after some hours the sound ones 

 have nearly all dispersed around the vessel, while the opaque are there 

 still, or have only succeeded in sticking to the wall of the basin, how- 

 ever small the bound required to overleap the barrier. Considering 

 the intensity and universality of the muscle infection, the diminution 

 of muscular vigor is quite natural; indeed, the surprising feature is 

 the relatively great agility retained by muscles the bulk of whose con- 

 tractile substance is much inferior to that of the parasite, and in some 

 cases it is truly astonishing that muscular power is not completely 

 destroyed. Among the diseased Paliemons no egg-bearing females 

 were seen. Perhaps this may be a case of '^ parasitic castration." The 

 diseased individuals do not survive very long, all succumbing by the 

 end of autumn, as during the winter not on« can be found. 



Conditions and mode of infection. — The prawns affected are usually 

 found in small shallow ditches containing a layer of water 0-10 m. to 

 0-20 m. deep, along the slope separating the compartments from the 

 salt marshes. The water of these ditches is rarely renewed and acquires 

 an elevated temperature. These are probably the conditions favorable 

 to the development of the parasite. It is difficult to decide whether 

 the parasite finds an entrance by way of the alimentary canal. Hen- 

 neguy seems to favor the contrary view, as the first lesions are found 

 at places remote from the digestive tract. 



Artificial infection. — Captive Pala3mons fed for several months with 

 diseased tissue showed no signs of infection. It was impossible to pro- 

 long the experiment to see whether infection would ultimately ensue 

 (Henneguy, 1888). P. rectirostris fed for mouths with diseased tissue 



