168 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



filaments (arraiijjed in two series, a and h below) tojiether with a con- 

 neetive tissue sheath [c below). 



{a) First series, composed of one yellow filament (variety 1) and two 

 white filaments (variety 2), the latter applied one along each side of 

 the yellow filament. One of the white cylinders is always flexuous, the 

 other always straight and without undulations. 



(b) Second series, consisting, like the first, of a yellow filament (vari- 

 ety 1) accompanied bj' two semitransparent, hyaline, whitish filaments, 

 which resemble the previously described filaments in being continuous 

 and endless, hut ichk'h appear not to he composed of cells. They consist 

 only of a thin wall filled with a semiliquid, finely granular substance. 

 One of these whitish filaments is fiexuous and undulating; the other, 

 instead of being straight throughout its whole length, undulates a 

 little from place to place. 



(e) Sheaths fiu-med of connective tissue of the host, jjenetrated by 

 delicate capillaries. 



Parasitic mass (as a whole). — Showing through the thin covering of 

 transparent mucous membrane of l)ranchial cavity as a grayish or 

 whitish mass of convoluted strings (varieties 1 and 2), strewn with small 

 brown masses (variety 3) of the size of a pea. Size of parasitic mass 

 varying from that of a millet seed to that of a large goose egg. Some- 

 times voluminous on one side and small on the other; sometimes com- 

 posed of two or three separate lobes. Form inconstant, generally con- 

 sisting of round or elongated lobes. Arteries and veins few, extremely 

 delicate; derived from vessels of neighboring muscles, which, with the 

 loose submucous tissue, form the only bond between the mass and the 

 tissues of the host. Injection with mercury (of the connective tissue 

 sheath, described above under variety 1) demonstrates that the mass 

 consists of closed lobules. When filled with mercury, no escape of the 

 metal occurs unless greater pressure j)roduces rupture. When very 

 small, the mass may be unrolled and shown to consist of a convoluted 

 string. 



Habitafj etc. — Submucous connective tissue of branchio-abdominal 

 septum (between scapular and last branchial arch) of Sciwna umbra. 

 Among 9 fish (male and female) examined in September, it was absent 

 in 4. The size of the 5 hosts varied from 1'30 m. to 1-70 m. Sometimes, 

 but rarely, variety 3 exists alone, the usual condition, however, being 

 that varieties 1 and 2 are present together and are accompanied by 

 small colonies of variety 3. 



Nature. — llobin regards it as referable to the Diatoms. Lieberkiihn^ 

 says that: 



The ijsorospernis of some marine fishes recently described by Robin behaA'e in 

 every respect like Trt^matode eg^^- 



Whatever other view be taken of its affinities, this specnes is cer- 

 tainly not myxosporidian. As remarked above (p. 72), the generic 

 name must follow the type species. 



> Mailer's Archiv., 1851, pp. 10-11. 



