THE MYXOSPORlDiA, OR PSOROSPERMg OF FISHES. 117 



SPKCiriC CHARACTERS. 



Sporc-form: This is a somewhat variable character, e. g., elliptic 

 spores, varying iu breadth; nevertheless, considerable dependence may 

 usually be ijlaced upon it. 



Tail: I have elsewhere (p. 207) indicated my belief that the presence 

 of a tail is a good specific character. The length of the tail relative to 

 that of the body (caudal index) will also prove useful. 



Eidge index: As the width of the ridge bears a very constant ratio 

 to the whole width of the surface of w^hich the ridge forms a i)art, this 

 ratio is a good specific character, especially as it often differs markedly 

 in different species. 



Capsular index: This is a character of great constancy, and hence of 

 much taxonomic value. 



Nuclei : The presence or absence of the pericornual nuclei has proved 

 constant in several species examined by me (see p. 210). The position 

 of the remaining nuclei is inconstant. 



VI.— PATHOLOGY. 



Pfeiff'er says ^ that rayxosporidian infection is characterized by the 

 rapid disappearance of the nuclei of the infected cells, the infection of 

 the red blood corpuscles, and the attacking of all the elemental tissues 

 of the host, with the possible exception of those of the nervous system; 

 further, through the early spore formation which is unconnected with 

 any external evidence of maturity. And, farther, considering how the 

 blood parasites of Emys. Laccrta, birds, and of malarially diseased cattle 

 and men, employ the blood-cori^uscle membranes as protective coverings 

 for their naked bodies; also, that the youngest myxosporidia, just 

 out of the spore shell, attack the red blood corpuscles; and, further, 

 that the Mijxospoi-UUa spare no organ or elemental cells (the nervous 

 system i)ossibly excepted), the destructiveness of this grouj) of para- 

 sites must be recognized to be very great; and, further, that the para- 

 site withdraws directly or indirectly a large quantity of blood from the 

 host, is shown by the hiiematoidin crystals found in all myxosporidia. 

 Finally, a cachexia, comparable with the cancerous cachexia of the 

 warm-blooded animals, is produced. 



By a reference to p. 187 it will be seen that Korotneff observed in 

 the polyzoan, Alcyonella fungosa, substantially the same process that 

 Pfeifter records in Lucius lucius, viz, an intracellular develoi^ment dur- 

 ing the earlier myxosporidium stages. 



Mode of infection. — Leydig^ remarked that an organism like Gen. 

 ineert. sp. 4. could pass with the blood current into tlie various organs, 

 efl^Bct a lodgment, become encysted, and give rise to the "psorosperms." 



'Die Protozoen als Kranklieitserreger, 1890, 1 ed., pp. 48-49; 2 eel., 1891, p. 135. 

 ^Miiller's Archiv, 1851, p. 229. 



