158 DR. T. S. COBBOLD ON ENTOZOA. 
In the Haddock and others of the Cod-family we meet with many kinds of Entozoa 
and the worms found in one species seem liable to occur in all members of the group. 
Most of the Trematoda infesting fishes are exceedingly minute, and it is absolutely neces- 
sary for their identification that specific descriptions should be accompanied with accurate 
figures. I am led to this remark from the difficulty of making out the identity of å 
Distoma found associated with Echinorhynchus acus, R., and Bothriocephalus rugosus, R,, 
in the intestine of a Haddock. The trematode in question agrees in some respects with 
D. scabrum and D. appendiculatum, especially the latter, but differs in a few essentials ; 
moreover, D. appendiculatum is not mentioned as infesting the Gadidæ. Provisionally 
therefore I propose to regard it as a distinct species, and shall briefly describe it under 
the title of D. rachion (paxiaioc), as follows (figs. 9, 10) :—Body of a faint pink colour; 
length 3 lines; flat, covered with minute spines; obtuse at either extremity ; posterior 
half of the body rather broader than the front; oral sucker large, not quite terminal; 
ventral sucker comparatively small, near the centre of the body; cesophagus narrow, 
twisted, bifurcating immediately above the ventral sucker ; gastric canals very capacious; 
genital pore large and conspicuous; internal seminal vesicle, uterine tube, ovary, testes, 
and contractile vesicle particularly distinct. Some other details in regard to the struc- 
ture of this trematode will be found indicated in the explanation of the accompanying 
figures. In regard to Bothriocephalus rugosus I have only to observe, that in conse- 
quence of the head being found in all instances firmly rooted within one of the pancreatic 
cæca, it was impossible to ascertain the precise form of the cephalic segment. Dujardin 
remarks the same peculiarity in specimens obtained by him from Gadus pollachius and 
G. merlucius. The single Echinorhynchus, obtained from the same Haddock, exhibited 
when alive an organ lying near the proboscideal sheath—the so-called lemniscus, con- 
cerning the use of which we are still ignorant. In common with others, I have observed, 
in another acanthocephalous species, two of these organs, one on each side of the sheath. 
They have no connexion with the retractor muscles; but the latter, in the example under - 
consideration, could not be recognized through the semi-opake integument. A Haddock _ 
examined by me on the 8th of May, 1854, contained, in addition to two specimens of the 
above-mentioned Bothriocephalus, several small cysts enclosing Filariæ, and a larger 
solitary cyst occupied by a Tetrarhynchus (figs. 11 to 19 inclusive). These require a 
passing notice. The minute sacs were imbedded in the submucous tissue of the aliment- 
ary canal, and scarcely exceeded half a line in breadth. The single large cyst, situated 
beneath the peritoneum outside the intestine, measured about a quarter of an inch long, 
and one-eighth of an inch broad. It was oval, semitransparent throughout, and on divi- 
sion of the peritoneal investment, easily removed. When detached, the fibro-cellular in- 
vesting capsule or ectocyst offered a pyriform outline, and from its narrow extremity there - 
proceeded a stalk-like prolongation. The ectocyst on being torn open disclosed the tetra- 
rhynchoid Scolez, the head and body of which were invaginated, but became readily evolved 
by gentle pressure applied to the bulky caudal vesicle or endocyst. Amplified forty dia- 
meters, the internal structures were well seen, the proboscidiform tentacula and * sclerous 
particles” being especially conspicuous. I have here, with due consideration, applied the 
term “sclerous” to the subcutaneous corpuscles so abundant in the caudal vesicle, in 
