Insects, birds, mammals, fish and amphibians, for example, all have an alimentary canal, or continuous through-gut, with an opening through which they eat, the mouth, and another opening for defecation.
The quiescent cells may be fated to become germ cells by maternally inherited determinants before, or immediately following, fertilization ("preformation" or "primordial germ cells"), as in amphibians, for example [ 35].
It is important to point out that PKR genes of fish, for example the three PKR genes of T. nigroviridis, and amphibians, for example the three PKR genes of X. tropicalis, while sharing a common ancestor, arose from independent gene duplications and should therefore be viewed as paralogs, not orthologs.
Amphibian declines, for example, have been associated with habitat loss, a barrage of novel enemies (diseases, predators and parasites), contaminants and climate change (Blaustein and Kiesecker 2002; Blaustein and Bancroft 2007).
Pupils will start with simple concepts of change, adaptation and natural selection illustrated by the evolution of fish to amphibians to mammals, for example.
There are lots of good sequences, from the amphibians to the mammals for example, or (in more detail) the evolution of the horse from Eohippus on five toes to the modern horse on one toe.
For example, amphibians like the olm that live in caves may be largely colourless as colour has no function in that environment, but they show some red because of the haem pigment in their red blood cells, needed to carry oxygen.
For example, amphibians are threatened by other causes such as chytridiomycosis, and although in some PAs various measures are being taken (e.g. use of Bioclean), it is very difficult to protect amphibians against this disease through any kind of land protection [57].
There is a reverse relationship between RBC size and metabolic rate among different groups of vertebrates: for example, amphibians display the largest genome sizes and blood cells along with a low metabolic rate while birds have relatively small genome size and RBC size with a high metabolic rate [ 69].
Others provide a mix of two classes – the rhino-like Grux and amphibian-gorilla hybrid Rampage, for example, are equally capable as melee fighters and tanks, though not quite as capable at either role as pure melee fighters and tanks.
Amphibian and reptilian anatomy, for example, is today mostly presented in the form of illustrative drawings and pictures [18] [20].
