The testes are paired; they are rarely single in Teleostei. The inactive organ is semi-transparent; the active organ varies much in size, shape, and lobulation, 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, etc. The ovary, as in some other Teleostei, is single. The ova is produced by lamellae arranged transversely. The oviducal canal is central in the Perch, etc, and lined by a flat or columnar epithelium. It is lateral in the Pike, Cyprinoidei, etc, 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.
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 Te/eostei, 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 material.
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, Gunther, 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. 1, 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.Leydig, Festschrift zur Feier des 100-jahrigen Bestehens der Naturf. Gessellsch. in Halle, 1879. Organs of Lateral Line. Merkel, Endigungen der sensibeln Nerven, Rostock, 1880; Bodenstein, Z. W. Z. xxxviii. 1882; Solger, Z. A. v. 1882; Leydig, op. cit. supra. Scales. Baudelot, A. Z. Expt. ii. 1873; Carlet, A. Sc. N. (6) viii. 1879; O. Hertwig, M. J. ii. 1876; v. 1879; vii. 1881.
Central nervous system.Mayser, Z. W. Z. xxxvi. 1882; Ussow, Archives de Biologie, iii. 1882 j Rabl-Ruckard, Arch. fur Anat. und Physiol., Anat. Abth. 1882, 1883; Id. Biol. Centralblatt, iv. 1884-85. Pineal gland. Cattie, Archives de Biologie, iii. 1882; Id. Z. W. Z. xxxix. 1884.
Organs of special sense.Nasal. Blaue, Z. A. v. 1882. Eye. Berger, M. J. viii. 1882; Hoffmann, A. M. A. xxiii. 1884. Ear. Retzius, Gehororgan der Wir-belthiere, i., Stockholm, 1881; for abstracts, see Biol. Centralbl. ii. 1882-83.
Teeth.Tomes, Ph. Tr. 166, 1876; Id. Dental Anatomy (ed. 2), London, 1882; Sternfeld, A. M. A. xx. 1882; in Scaroids, Boas, Z. W. Z. xxxii. 1879; cf. Owen, Odontography, Text and Atlas, London, 1840-45.
Digestive tract: minute anatomy. Edinger, A. M. A. xiii. 1877; physiology, cf. Krukenberg, Vergleich. Physiol. Vortrage, ii. Heidelberg, 1882; in Cobitis fos-silis, Lorent, A. M. A. xv. 1878. Pancreas, Legouis, A. Sc. N. (5) xvii, and xviii. 1873. Pharyngeal pouches, rumination, of Scaridae. Sagemehl, M. J. x. 1885.
Air-bladder: minute anatomy. Schulze, Stricker's Histology (Sydenham Soc), ii. 1872, p. 78. Function. Moreau, A. Sc. N. (6), iv. 1876.
Branchiae: minute anatomy. Riess, A. N. 47, 1881. Pseudo-branchia. Maurer, M. J. ix. 1883.
Heart.Kasem-Beck und Dogiel, Z. W. Z. xxxvii. 1872. Conus. Boas, M. J. vi. 1880.
Spleen (in Ichthyopsidd).Phisalix, A. Z. Expt. (2) iii. 1885.
Lymphatics.Sappey, Systeme lymphatique des Poissons, Paris, 1880.
Thyroid and Thymus (with development).Maurer, M. J. xi. 1885.
Kidneys.Hyrtl, Dk. Wien. Akad. i. 1850; ii. 1851. Balfour, Q. J. M. xxii. 1882; Emery, Archives Italiennes Biol. ii. 1882, cf. Furbringer, M. J. iv. 1878. Head-kidney. Grosglik, Z. A. viii. 1885; ix. 1886; Emery, Ibid. Renal-portal circulation. Jourdain, A. Sc. N. (4) xii. 1859.
Sex organs.Brock, M. J. iv. 1878. Oviducts of Osmerus. Huxley, P. Z. S. 1883. Development of Duct. MacLeod, Archives de Biologie, ii. 1881; in Lepi-dosteus, Balfour, and W. N. Parker, Ph. Tr. 173, 1882.
Fishes ova.Mcintosh, Nature, xxxi. 1884-85. Relations of Yolk to Gastrula in Teleostei. J. T. Cunningham, Q. J. M. xxvi. 1885-86.
Parasites of fresh-water Fish.Zschokke, Archives de Biologie, v. 1884.