What is a
reptile?

A reptile is a vertebrate which,
like amphibians, is ectothermic, its body temperature influenced by the
temperature of its surroundings. Its body is covered with dry skin, from
which grow scales.

   Body wastes, eggs
and sperm all leave the body of a reptile through the final section of
the gut, which is called the cloaca. A reptile's kidneys can change body
wastes from liquid to solid form. Land reptiles' urine forms part of the
limy waste material passed out of their bodies, but aquatic reptiles
usually pass fluid urine as well as solid wastes.

   The sperm produced
by a male reptile fertilizes a female's eggs inside her body (in
amphibians, fertilization takes place outside the body). The fertilized
eggs of most reptile species are enclosed in shells and are laid on
land. However, some species retain their eggs within their bodies until
the young hatch.

   Most reptiles eat
other animals, though a few eat plant material.

   Most reptiles have
four limbs. Snakes have no limbs (though pythons have remnants), and
some lizards have reduced limbs, only two hind limbs, or scaly flaps
instead of hind limbs.

Lungs and hearts

When it breathes, a reptile
expands its ribs, drawing air into its lung. After oxygen and carbon
dioxide have been exchanged in the lungs, the reptile breathes out by
contracting its ribs. In a few water-living species, some exchange of
gases takes place through the skin or even the cloaca.

Turtles, lizards and snakes have
three-chambered hearts. In the single lower chamber, oxygenated blood
coming from the lungs may mix with deoxygenated blood from the body.

Crocodiles have four-chambered
hearts, like those of birds and mammals. Normally oxygenated and
deoxygenated blood do not mix, but during a long dive, when fresh air is
not available, a special valve allows deoxygenated blood to pass back
into the crocodile's body tissues.

Desert survivors

Australia's many dry areas are
full of reptiles which are adapted to arid conditions in a number of
was:

·Their
body wastes have very little water in them.

·They
obtain water from their food, and from licking dew. The scales of some
lizards channel water to the mouth.

·Because
of their low energy requirements, reptiles can survive food scarcities
during drought.

·Small
reptiles feed on ants and termites, which are plentiful in the desert.
The small reptiles are then eaten by larger reptiles.

·A
reptile becomes active when the temperature is right for its species. In
the desert, it may forage at night, and shelter in a burrow during the
day, or spend daytime shuttling from sunshine to shade and back again.
Some lizards climb some distance off the ground into vegetation to avoid
ground heat.

Wetlands predators  

The floodplains of northern
Australia support a greater weight of predators in a given area than do
Africa's Serengeti Plains.

The African predators are
mammals such as lions and hyenas. The Australian ones are reptiles, such
as water-living pythons, file snakes, freshwater turtles, crocodiles and
a variety of lizards, including the Frilled Lizard. These creatures eat
each other, as well as insects and other invertebrates, fish, frogs and
small mammals.

什么是爬虫？

爬虫是脊椎动物，它像两栖类一样属冷血动物，它的体温受周围气温影响。它身体表面有一层干燥的皮，鳞片就是从这层皮上长出的。

爬虫体内的废物﹑卵子和精液全都通过被称为泄殖腔的直肠的最后一段排出。爬虫的肾脏能将体内的废物从液体转变为固体。陆生爬虫的小便转化成粘性排泄物的一部分排出体外，而水生爬虫通常既排固体泄物也排液体泄物。

公爬虫产出的精子在母爬虫的体内与卵细胞受精（在两栖类动物中，受精在体外进行）。大多数爬虫的受精卵被包在蛋壳里，并且产在陆地上。不过，有些种类的爬虫把它们的受精卵留在体内直到孵出幼爬虫。

尽管少数爬虫以植物为食，但大多数爬虫以其它动物为食。

大多数爬虫有四条腿。蛇没有腿（尽管蟒蛇有腿的残留物），一些蜥蜴拥有退化的腿，或只有两条后腿，实际上是带鳞的垂下物而谈不上是后腿。

肺和心脏

当爬虫吸气时，它撑开肋骨，把空气吸进肺中。氧和二氧化碳在肺中被交换后，它收缩肋骨呼气。在少数水生种类中，气体交换通过皮肤甚至泄殖腔进行。

龟﹑蜥蜴和蛇的心脏有三个腔。在位于下方的单心室中，来自肺部的动脉血会与来自躯体的静脉血混合。

像那些鸟和哺乳动物一样，鳄鱼的心脏拥有四个腔。通常动脉血和静脉血不混合，但长时间潜水期间，鳄鱼不能得到新鲜的空气时，一个专用的瓣膜会让静脉血回流到鳄鱼的身体组织中。

沙漠幸存者

澳大利亚的许多干旱地区充满了爬虫，它们适应干旱的环境，它们有以下一些身体特征：

·它们的排泄物中几乎不含水分。

·它们从食物和露水中获取水分。有些蜥蜴甚至会用鳞片将水引到口中。

·由于它们极低的能量需求，使它们能在食物缺乏的干旱环境中生存下来。

·小爬虫靠蚂蚁和白蚁充饥，沙漠里有许多这些小动物。随后小爬虫又被大爬虫捕食。

·爬虫在气温适宜季节活动频繁。在沙漠，爬虫夜间觅食，白天却躲在地洞，或者整个白天在日光地与阴凉处之间跑来跑去。有些蜥蜴离开地面爬到植被上以避免地面的日晒。

沼泽地掠食者

生活在澳大利亚北部洪泛平原的某一地区的掠食动物比生活在非洲塞伦盖提大草原上的）掠食动物多。

非洲的掠食动物是像狮子和鬣狗一类的哺乳动物。而澳洲则生活着下列爬虫，例如水蟒﹑瘰鳞蛇﹑淡水龟﹑鳄鱼以及包括皱褶蜥在内的大量蜥蜴。这些动物以同类为食，也吃昆虫﹑无脊椎动物﹑鱼﹑青蛙和小哺乳动物。

顾纯豪
翻译