PISCES. 
with a similar marsupial apparatus, in which 
the eggs are hatched and the young permitted 
to arrive at their full developement prior to 
their expulsion. These are the Syngnathida, 
or pipe-fishes. There is, however, this remark- 
able difference between the mammiferous mar- 
supials and these singularly organized genera, 
namely, that in the former it is the female that 
is furnished with the marsupial pouch, whereas 
in the Syngnathide the male only is so pro- 
vided. In fig. 539, representing the male of 
Syngnathus acus, the marsupial apparatus is 
well exhibited ; it consists of two large valves 
(m) situated beneath the tail, immediately pos- 
terior to the cloacal orifice. The internal sur- 
face of this pouch is indented with deep cells 
(0, 0), more especially towards its posterior 
surface, where the ova are principally lodged. 
Here the eggs are hatched, after which the 
young Syngnathi are retained in the pouch for a 
considerable period before they are finally ex- 
elled. 
° In the female Syngnathus there is no sub- 
caudal pouch developed, but in this sex the 
vulvais unusually prominent, apparently for the 
purpose of facilitating the conveyance of the 
ova into the marsupium of the male. 
In Syngnathus ophidion (Bloch) the ova, 
after extrusion from the female and impregna- 
tion, become attached to the cellular surface of 
the ventral parietes of the abdomen of the male, 
but are not protected by cutaneous processes or 
valves. 
Urinary apparatus.—The kidneys in Fishes, 
as in all other Vertebrata, are two in number, 
situated on each side of the spine. They 
are, however, in the class before us remarkable 
for their very great proportionate size, some- 
times extending from the anterior boundary 
of the abdomen quite to its posterior ex- 
tremity, and occasionally uniting together in 
the mesial plane, so as to have the appearance 
of being but a single gland. Internally they 
present no division into cortex and fasciculate 
ducts terminating in a pelvic cavity, but their 
parenchyma is homogeneous, being entirely 
composed of arborescent ducts, which are im- 
mediately continuous with the ureters, which, 
running along the anterior surface of the kidney, 
receive the uriniferous tubes as they pass along 
towards the cloaca, where they terminate. Most 
commonly there is a distinct urinary or allan- 
toid bladder situated behind or dorsad to the 
1011 
rectum (fig. 539, f), which, in some spe- 
cies, is bifid at the anterior extremity, as in the 
Frog and other amphibia. 
Occasionally the urinary canals unite and 
terminate by a common duct (ureter) upon a 
fleshy tubercle or penis-like projection of the 
walls of the cloaca, as in the female Shark 
(fig. 538, t.), where a bristle is represented in- 
troduced into the extremity of the urinary 
passage. 
Renal capsules —In the osseous Fishes these 
organs are supposed to be represented by two 
or sometimes three roundish bodies of a light 
grey colour, situated sometimes near the mid- 
dle, oftener at the hinder extremities of the 
kidneys, at or near the entry of the hemal 
canal; sometimes they lie free, sometimes they 
are imbedded in the renal tissue (Pike, Salmon, 
Eel); but they always possess a proper cap- 
sule and present a minutely granular texture 
without distinction of cortical and medullary 
parts.* In the yellowish suprarenal bodies of 
the Sturgeon, the granules are minute spherical 
cells filled by microscopic nucleated corpuscles. 
In the Plagiostomes they are represented by 
elongated narrow yellowish bodies situated be- 
hind the kidneys, and sometimes extending be- 
hind the dilated ureters. 
BIBLIOGRAPHY. — Cuvier, Legons d’anatomie 
comparée, 8vo. 1846. Cuvier et Valenciennes, His- 
toire naturelle des poissons, 4to. 1828. Haller, 
Opera minota, vol. iii. Monro, Structure and phy- 
siology of Fishes, fol. 1785. Observations on the 
organ of hearing in man and other animals, 4to. 
1797. Scarpa, De auditu et olfactu, fol. 1789. 
Comparetti de aure interna comparata, 4to. 1789. 
Hewson, Phil. Trans. vol. lix. Cavolini, Memoria 
sulla generazione dei pesci e dei granchi, 4to. 1787. 
Autenrieth, Anatomie de la plie. | Wiedemann’s 
Archiv, tom. i, 1800. Geoffroy St. Hilaire, An 
nales des Museum d’Hist. Nat. t. ix. & x. Rosen- 
. thal, Ichthyomische Tafeln, 4to. 1812-22. Spix. 
Cephalogenesis, fol. 1815. Carus, Lehrbuch der 
Zootomie, 8vo. et 4to. 1818. Erlanterungs-tafeln 
zur vergleichenden anatomie, fol. 1826. Weber, 
De aure et auditu. Van der Heaven, Dissertatio 
philosoph. de sceleto piscium, 8vo. 1822. Bakker, 
Osteographia piscium, 4to. 1822. Meckel, Traité 
d’anat comp. 8vo. 1828-9. Owen, Lectures on com- 
parative anatomy, Lond. 1847, 
* Owen’s Lectures, (Pisces, p. 285.) 
T. Rymer Jones.) 
PLACENTA. 
See Ovum (Supplement ) 
and Urerus. 
