= ABDOMINAL PORES 401 
a single main duct opening into the terminal part of the meso- 
nephric duct, and these tubules and their separate duct are 
sometimes regarded as a metanephros and a metanephric duct. 
The mesonephric nephrostomes are persistent throughout life in 
a few Elasmobranchs (e.g. Notidanidae, Heterodontidae, Rhinidae, 
and some Scylliidae), and also in Amia:' in all other Fishes 
as well as in the Cyclostomes they become closed in early 
life. 
In many Fishes the hinder extremity of the coelom com- 
municates directly with the exterior through “abdominal pores,” 
of which there is usually a 
pair, rarely a single pore, 
situated close to the cloacal 
or the anal aperture.” Elasmo- 
branchs usually have a_ pair, 
often at the extremities of a 
pair of cloacal papillae (Fig. 
231), but they are absent in 
some families (eg. Hetero- 
dontidae and Rhinidae); and 
in some Scylliidae (e.g. Seyl- 
lium canicula) they are very 
variable, being either present 
or absent on both sides, or an LY, 
open pore 1S present on one Fig. 231.—Diagrammatic horizontal section 
side only. Pores are present through the abdominal pores and cloaca 
of an Elasmobranch. «a@.p, Abdominal 
and paired in the Crosso- pore ; c, coelom ; c/, cloaca; cl.p, cloacal 
pases \ Sii8 papilla; ¢.p, cloacal pit; od, oviducal 
pterygu, the Chondrostei, and apertures in the female; 7, rectum; 
the Holostei. Amongst the u.s, cloacal aperture of the urinary sinus 
Di : Ne “afodas i nce (female), or the urogenital sinus (male). 
a CCUG aS 2 pall In some Elasmobranchs the abdominal 
of pores. Protopterus some- pore opens at the base of the cloacal 
. ? aes papilla, as shown at a.p'. (Modified from 
times has two pores opening Bles.) 
into the cloaca, but as a rule 
the two become confluent and have a single external aperture. 
In Lepidosiren pores are wanting. Abdominal pores are rarely 
present in Teleostei. They exist, however, in the Mormyridae 
(Gymnarchus and several species of Mormyrus), and also in the 
1 Jungersen, Zool. Anz. xxiii. 1900, p. 328. 
* Bridge, Journ. Anat. and Phys. xiv. 1879, p. 81; Bles, ib. xxxii. 1898, p. 
484; Proc. Roy. Soc. lxii. 1898, p. 232. 
VOL. VII 2D 
