COMMON PERCH. 83 



Skull of Frog. Id. Ph. Tr. 161, 1871 ; cf. Parker and Bettany, The Morpho- 

 logy of the Skull, London, 1877. Basioccipital. Albrecht, Bull. Mus. Hist. Nat. 

 Belg. ii. 1882-83. 



Vertebral column. Gegenbaur, Untersuchungen zur Vergleich. Anat. derWirbel- 

 saule bei Amphibien und Reptilien, Leipzig, 1862. Urostyle. Gotte, Entwickelungs- 

 geschichte der Unke (Bombinator igneus\ Leipzig, 1875, with Atlas, p. 391. Ribs. 

 Gotte, op. cit. p. 381. 



Sternum and shoulder-girdle. Gotte, A. M. A. xiv. 1877. 



Pelvis. Hoffmann, Niederland. Archiv. fur Zool. iii. 1876-77. 



Carpus and Tarsus. Gegenbaur, Untersuchungen zur Vergleich. Anat. der 

 Wirbelthiere i., Leipzig, 1864. 



Sixth Toe. Born, M. J. i. 1876; vi. 1880, p. 49. Structure of toes, &c. Leydig, 

 M. J. ii. 1876. 



1 6. THE COMMON PERCH (Perca fluviatilis)> 



Dissected so as to show its nervous, respiratory, circulatory, digestive, and 

 reproductive systems in situ. 



THE following external characters are to be noted : the laterally 

 flattened body and pointed head : the general investment of cycloid scales : 

 the conformation of the mouth : the large eye devoid of eyelids ; and the 

 two dorsally placed apertures, anterior and posterior, of the nose, neither of 

 them communicating with the mouth : the lateral line of sensory organs 

 extending down each side of the body to the tail, and the four depressions 

 on the under surface of each lower jaw indicating the position of the sense 

 organs contained within one of the so-called mucous canals of the head : 

 the opercular apparatus, composed of the operculum and the branchiostegal 

 membrane with its supporting rays which cover the branchial arches 

 laterally and meet on the ventral surface under the chin : and the two sets 

 of fins, azygos and paired. The former consist of the two dorsal, the 

 caudal and the anal fins, imperfectly seen in this specimen, because the 

 caudal region has been removed and the body cut through about the 

 middle of the second dorsal and the anal fins. The paired fins are to be 

 seen on the left side the pectoral above, i.e. dorsally, and -the ventral below. 

 A line drawn through the attachment of the pectoral fin, and at right angles 

 to the long axis of the body, passes just in front of the ventral fin ; the latter 

 is therefore said to be thoracic in position. When such a line passes behind 

 the ventral fin, the latter is said to be jugular in position. In a certain 

 group of Teleostei which preserves the duct to the air-bladder and is hence 

 termed Physostomi, the ventral fins are placed somewhat in front of the 

 anus, but remote from the pectoral, and are then said to be abdominal, 

 e.g. Pike, Salmon. 



The brain and viscera have been exposed in situ by the removal of the 



G 2 



