Common Perch. 41 



homologous with i\\e fossa cystis felleae of anthropotomy, but with 

 which the g-all-bladder of this fish does not come into relation 

 when the ovary is not in a state of turgescence. 



The rectum, on the other hand, is seen commencing, as in so many 

 vertebrate animals, in close proximity to the commencement of the 

 small intestine, and passing with a straight course down the middle 

 line of the body to terminate, as in fishes only, in an anus placed an- 

 teriorly to the openings of the urinary and generative ducts. In the 

 peritoneal lamellae which connect the rectum with the ovary, and 

 also along the outer side of the air-bladder, are seen bands of yellow- 

 coloured pellets of fat in a condition of atrophy correlated with the 

 hypertrophy of the ovary. In the glistening walls of the air- 

 bladder may be seen its vaso-ganglia. Between the upper end of 

 this organ and the hiudermost gill is seen a gland placed homo- 

 logously to the thymus of the Frog, and resembling the spleen 

 both in its naked eye, and in its microscopic appearances. The 

 upper end of the kidney is separated from this gland by a fibrous 

 partition, and its entire length, corresponding with that of the 

 abdominal cavity, is concealed by the air-bladder below it. Im- 

 mediately in front of the dorsal end of the first true gill is placed 

 the uniserial pseudobranchia. 



The four divisions of the encephalon are in apposition with, but 

 do not overlap, each other in any case from before backwards ; 

 they fall far short of filling the cranial cavity, whence much cellular 

 tissue, richly laden with oleaginous matter, has been removed. The 

 optic lobes are the largest of the four ganglionic centres; they 

 are, like the prosencephalon and rhinencephalon, paired, whilst the 

 sub-glo1)ular cerebellum is unpaired. 



The large size of the eyes, and the bilateral pairing of the nasal 

 orifices, which do not communicate with the digestive tract, are 

 characteristically piscine peculiarities, though not universally found 

 in members of the class. 



The membranous valve projecting backwards into the mouth 

 from the under surface of the upper jaw deserves notice. 



A series of scales, perforated Ijy mucous ducts supplied with 

 nerves, forms a ' lateral line '' along the trunk, the contour of which 

 corresponds with that of the upper line of the back, beginning 

 with the bone called by Cuvicr ' surscapulairc' (Hist. Nat. des 

 Poissons, i. 274), but recognized by him (1. c. p. 273.), as also by 



