NeXT APODES 599 
of fillimg with air immediately derived from the atmosphere. 
Although covered over by the common integuments, these bladders 
present externally, when inflated, two protuberances of a round 
shape. Of the whole volume of blood contained in the branchial 
artery, one-third passes through the gills and respiratory bladders, 
whilst the other two-thirds are conveyed directly from the heart 
to the aorta without being exposed to the action of the air.' 
This amphibious Fish, when in the water, constantly rises to the 
surface for the purpose of respiration, and it is often found lying 
in the grassy sides of ponds after the manner of Snakes. 
Sub-Order 4. Apodes. 
Air-bladder, if present, communicating with the digestive tract 
by a duct. Praemaxillaries absent; the maxillaries, if present, 
separated on the median line by the coalesced ethmoid and 
vomer. Pectoral arch, if present, not connected with and remote 
from the skull; mesocoracoid arch absent. Fins without spines, 
the ventrals absent. Anterior vertebrae distinct, without Weberian 
ossicles. 
‘The Apodes or Eels are elongate, serpentiform Fishes with 
naked skin, or with minute scales imbedded in the skin, the 
opércular bones small and completely hidden under the integu- 
ment ; narrow or minute gill-openings; the vertical fins, if 
present, confluent behind or separated by the projecting tip of the 
tail. The pterygo-palatine arch is often reduced or absent, and 
there is no distinct symplectic ; the supraoccipital bone is small, 
separated from the frontals by the parietals, which meet on the 
middle line. The vertebrae are very numerous (up to 225), and 
the praecaudals bear strong parapophyses, to which short, slender 
ribs may be attached; epineurals are sometimes present. The 
five families into which this sub-order is divided show remarkable 
degrees of simplification of the skull, through reduction or loss 
of either the maxillary or the pterygo-palatine arches. 
There has been much difference of opinion in the determina- 
tion of the bones of the upper jaw in these Fishes. Cuvier regarded 
the lateral bones of the upper jaw as praemaxillaries, Owen and 
Richardson as palatines (at least in Muraenas), whilst Peters 
1 Cf. Taylor, Edinb. Journ. Sei. v. 1831, p. 33; Hyrtl, Denkschr, Ak. Wien, 
xiv. 1858, p. 39. On the osteology, ef. Gill, Proc. U.S. Nat. Mus, xiii. 1890, p. 299. 
