342 Diseases of Fishes 



The relation of this crustacean to its host suggested to Latrobe, 

 its discoverer, the relation of the ' ' f oretaster " in Roman times 

 to the tyrant whom he served. A similar commensation exists 

 in the mouth of a mullet (Mugil hospes) at Panama. The 

 writer has received, through the courtesy of Mr. A. P. Lundin, a 

 specimen of a flying-fish (Exonautes unicolor) taken off Sydney, 

 Australia. To this are attached three large copepod crustaceans 

 of the genus Penella, the largest over two inches long, and to 

 the copepods in turn are attached a number of barnacles (Con- 

 choderma virgatum) so joined to the copepods as to suggest 

 strange flowers, like orchids, growing out of the fish. 



Myxosporidia, or Parasitic Protozoa. Internal parasites are 

 very numerous and varied. Some of them are bacteria, giving 

 rise to infectious diseases, especially in ponds and lakes. Others 

 are myxosporidia, or parasitic protozoans, which form warty ap- 

 pendages, which burst, discharging the germs and leaving ulcers 



FIG. 227. Black-nosed Dace, Rhinichthys atronasus (Mitchill). East Coy Creek, 

 W. N. Y. Showing black spots of parasitic organisms. 

 (From life by Mary Jordan Edwards.) 



in their place. In the report of the U. S. Fish Commissioner 

 for 1892, Dr. R. R. Gurley has brought together our knowl- 

 edge of the protozoans of the subclass Myxosporidia, to which 

 these epidemics are chiefly due. These creatures belong to the 

 class of Sporozoa, and are regarded as animals, their nearest 

 relatives being the parasitic Gregarinida, from which they differ 

 in having the germinal portion of the spore consisting of a 

 single protoplasmic mass instead of falciform protoplasmic 

 rods as in the worm-like Gregarines. The Myxosporidia 

 are parasitic on fishes, both fresh-water and marine, especially 

 beneath the epidermis of the gills and fins and in the gall- 

 bladder and urinary bladder. In color these protozoa are 



