COMMON PERCH. 89 



according to its state. The vas deferens, as in all Acanthopteri, lies on the inner 

 (median) side of the gland in a well-marked hilus. It becomes free posteriorly, 

 and fuses with its fellow. In the genus Blennius the two remain unfused. The 

 mesorchium in the Perch is single at its origin, a rare abnormality. The tubuli semi- 

 niferi are long, simple, and radially arranged at the hilus. In the Pike they form 

 numerous anastomoses inter se, as in Cyprinoidei, Clupeidae, &c. The ovary, as in 

 some other Teleostei, is single. The ova is produced by lamellae arranged trans- 

 versely. The oviducal canal is central in the Perch, &c., and lined by a flat or 

 columnar epithelium. It is lateral in the Pike, Cyprinoidei, &c., and lined by 

 a ciliated epithelium. When there are two oviducts they unite posteriorly. The 

 genitalia are covered externally by a layer of flat epithelium which, according to 

 Brock, is peritoneal. The genital and urinary ducts open into a urogenital sinus 

 placed behind the anus, the former in front of the latter. In some instances the 

 oviducal aperture is situate on an enlongate papilla, e. g. in Rhodeus amarus, which 

 lays its eggs in the mantle cavity of the Anodon. In this instance the urinary 

 bladder opens also on the papilla. 



NOTE. On the ovary of Teleostei. In Salmonidae and the Eels the ova are 

 shed into the abdominal cavity, and pass out thence through pores, usually but 

 perhaps not properly homologised with abdominal pores. In the Smelt (one of 

 the Salmonidae] there are two oviducts widely open at their inner and anterior end, 

 just as in the majority of Ganoidei. Each ovary has developed from its ventral 

 edge a lamella, which curves over and partially protects the outer side of the ovary. 

 In all other Teleostei, as in the Perch, the ovaries and oviducts are continuous, and 

 this is true also of the Ganoid Lepidosteus. In the case of this fish, however, 

 Professor Balfour and Mr. W. N. Parker found that a lamella similar to that of 

 Osmerus was formed from the ventral edge of the ovary, and met another lamella 

 growing from the dorsal abdominal wall. These two lamellae by their union clearly 

 bring about the disposition of parts seen in the adult. Observations on the mode 

 of formation of the posterior part of the oviduct were not made for want of mate- 

 rial. The same want prevented MacLeod carrying his observations on Teleostei to 

 a perfect conclusion, but he has found with reference to the ovary a state of things 

 similar to what obtains in Lepidosteus. It remains to be ascertained whether the 

 ducts, generally called ducts of Miiller in Ganoids, are really so or not ; whether the 

 ducts of Teleostei are ducts of Miiller continuous with the ovarian capsule or not; 

 and whether in both groups alike the oviducts are not simply peritoneal folds 

 and nothing more. 



Study of Fishes, Giinther, Edinburgh, 1880, or Id. Ichthyology, Encyclopaedia 

 Britannica (ed. ix). xii. Pisces, Von Siebold and Stannius, Handbuch der 

 Zootomie, i. Berlin, 1854. Pisces, Hubrecht und Sagemehl, Bronn's Klass. und 

 Ordn. des Thierreichs, vi. i. (in progress). 



Perca fluviatilis. Fishes of Great Britain and Ireland, F. Day, i. p. 2, 

 London, 1880. A History of British Fishes, W. Yarrell, i. p. i, London, 1841 

 (ed. 2). 



Perch. Cuvier et Valenciennes, Histoire des Poissons, ii. p. 28, Plates 

 i-viii. Cod. T. J. Parker, Zootomy, London, 1884. 



Integument. Ley dig, Festschrift zur Feier des loo-jahrigen Bestehens der 

 Naturf. Gessellsch. in Halle, 1879. Organs of Lateral Line. Merkel, Endigungen 



