340 PHILOSOPHY OT ZOOLOGY. 



In the sturgeon^ an organ is found, in its internal structure, 

 similar to those intestinula ; but in its outward form re- 

 sembling the pancreas of the skate. It is inclosed in a 

 muscle, evidently intended to express its contents. It opens 

 into the intestine by three large orifices, and has internally 

 a singular reticular appearance, as exhibited by MONRO, in 

 his work on fishes, page 84. tab. ix. The character for the 

 discrimination of the species furnished by the appendices, is 

 of importance, as being easily investigated and permanent. 



These intestines* and the rest of the viscera situated in 

 the cavity of the abdomen, are contained in a membrana- 

 eeous sac or peritoneum. This is silvery in some fishes, 

 black or spotted in others. WILLOUGHBY observed, that 

 this sac opens externally near the anus, by means of two 

 small holes. These openings were afterwards examined by 

 MONRO, who found in each of these passages a semilunar 

 membrane or valve, so placed as to allow liquors to get out 

 from the abdomen readily, but to resist somewhat their en- 

 try into it. They serve for the exit of the eggs. 



The anus in fishes occupies many different positions, ac- 

 cording to the species. This circumstance was seized upon 

 by SCOPOLI, in the construction of his system of classifica- 

 tion, and was raised to the dignity of a primary character. 

 This orifice is not merely the opening, whence issues the 

 faeces, but frequently the spawn also. 



The liver in fishes is remarkable on account of its size, 

 in proportion to the rest of the body. It commonly lies al- 

 most wholly on the left side. Its colour exhibits various 

 shades of brown, frequently mixed with yellow. It abounds 

 in oil. It i& entire in some fishes, as the lamprey, flounder, 

 and salmon ; or divided into two or more lobes, as in the 

 perch and carp. These varieties of form are constant in 

 all the individuals of the same species, but frequently dif- 

 fer somewhat in the species of the same genus. 



