The Cambridge natural history, Vol. 08 (of 10)Gadow, Hans
Science
The Cambridge natural history, Vol. 08 (of 10)
Gadow, Hans
Animals
_Ichthyophis glutinosa_ extends from the slopes of the Himalayas to Ceylon,
the Malay islands, and into Siam. A second species, _I. monochrous_, occurs
in Malabar, Malacca, Borneo, and Java. _I. glutinosa_ reaches about one
foot in length, with a greatest thickness of a little more than half an
inch. The general colour is dark brown or bluish black, with a yellow band
along each side of the body.
This species has been studied extensively by the Sarasins.[43] It breeds in
Ceylon after the spring monsoon. The ovarian egg is oval, measuring 9 by 6
mm. The yolk is yellow; the blastoderm lies towards one of the poles. The
strong vitelline membrane becomes surrounded in the oviduct by a dense
albuminous membrane, which forms twisted chalazae, just like those of
birds' eggs, and by these two cords the eggs are strung together. Around
all this lies another mantle of albumen. The female digs a hole close to
the surface in moist ground near {91}running water, and there lays about
two dozen eggs. The egg-strings become glued together, entangled into a
bunch, and the female coils herself round the bunch and remains in that
position, probably to protect the eggs against other burrowing creatures,
as blind snakes (_Typhlops_ and _Rhinophis_) and certain limbless lizards,
with which the ground literally swarms. During this kind of incubation the
eggs assume a round shape, and grow to twice their original size, and the
mature embryo weighs four times as much as the newly laid egg.
[Illustration: FIG. 15.–_Ichthyophis glutinosa_ × 1. (After P. and F.
Sarasin.) 1, A nearly ripe embryo, with gills, tail-fin, and still with a
considerable amount of yolk; 2, female guarding her eggs, coiled up in a
hole underground; 3, a bunch of newly laid eggs; 4, a single egg, enlarged,
schematised to show the twisted albuminous strings or chalazae within the
outer membrane, which surrounds the white of the egg.]
The external gills are delicately fringed and red, and they move up and
down in the fluid of the egg. The body of the embryo is at first white, but
becomes pigmented with dark grey. A strong line of lateral sense-organs is
formed, and a ring of them lies around the eye and others on other parts of
the head. The short tail develops a fin. Of the three pairs of gills the
third is the shortest, and is generally turned dorsalwards. In embryos of 4
cm. in length the longest gill measures as much as 2 cm. Yolk is still
present in embryos which have reached the surprising length of 7 cm. Then
the gills begin to shrink a little, and at this time one pair of
gill-clefts breaks through at the base of the third external gill.
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