The latter has developed from the amphigastrula of the ganoids and dipneusts, whereas the discoid amniote gastrula has been evolved from the amphibian gastrula by the addition of food-yelk.
The teeth of the Devonian ganoids show a complicated folded structure.
In the Cretaceous the teleosts, or bony fishes, made their appearance, while ganoids declined toward their present subordinate place.
To the same physiological category belong the digestive diverticula of the intestinal canal, such as the pyloric appendices of the midgut found in many teleosts and ganoids (cf.
A second modification of the intestinal canal, suggesting the same physiological interpretation as the ileo-colic caecum, is presented by the so-called pyloric caeca or appendices of many Teleosts and Ganoids already referred to (p.
On the other hand in the Ganoids and in many Teleosts longer or shorter finger-shaped diverticula of the midgut are found immediately beyond the pylorus in the region of the bile-duct.
A group of fishes usually known as ganoids and which comprise the lung fishes of the Nile, of Australia, the garpikes of North America and the sturgeons, were very abundant during the closing days of the Silurian.
The ganoids most nearly like our modern sturgeons increased during the last of the Devonian and retained their prominence to the close of the Carboniferous.
The sturgeons and ganoids decreased throughout the Tertiary or Quaternary until at present we have but few living species.
Many ganoidsbecame extinct, but other ganoids came into existence to take their places.
In the ganoids the tail vertebrae decrease gradually in size and curve upwards in the upper lobe of the tail.
In the ganoids the upper lobe of the tail fin is the largest.
One of the important differences between the ganoids and the teleosts or true fishes is in the tail vertebrae.
All of our modern fishes except the few ganoids are more or less specialized.
The tail of all early ganoids was strongly heterocercal.
Of the large group ofGanoids so abundant during all these geological ages but few forms are living to-day.
Most of the sharks lived in the sea continuously, but the ganoids frequenting the coastal waters appear to have migrated inland.
Amongst the Teleostomes the lower ganoids show a similar development of longitudinal rows of valves in the conus.
In the Teleostomes, with the exceptions of those ganoids mentioned, the expanded bases of the arcualia undergo complete fusion to form cartilaginous centra which, unlike the chordacentrous centra, lie outside the primary sheath (figs.
Ganoids differ from all the other osseous fishes, and agree with the Plagiostomes, in the structure of the heart.
In the Upper Permian the Holostean ganoids (Acanthophorus) make their appearance, and the group becomes dominant in the Jurassic and the Lower Cretaceous.
In the actinopterygian Ganoids a well-developed testicular network is present; e.
These ganoids were allied to the Lepidosteus, or Gar-pike, of the American rivers.
This same genus of fresh-water ganoids has also been met with in the Hempstead beds in the Isle of Wight.
As the reptiles establish themselves on the land and in the waters, the Ganoids diminish, but the Sharks hold their own.
Further, the modern Ganoids and Dipnoi are mostly fresh-water animals, though the Sharks are largely pelagic.
The Ganoids and Dipnoi still, however, occupy a very important place through the Mesozoic ages (Fig.
The first fishes that we certainly know are the Ganoids and Sharks, which appear near the close of the Upper Silurian, in the English Ludlow for example (Fig.
The Ganoids found here all belong to an extinct group, characterised by the covering of the head and anterior part of the body with large bony plates.
In the Devonian age the Ganoids and Sharks, thus introduced in the Silurian, may be said to culminate.
This is especially the case with the Ganoids and the Dipnoi.
Selachians and Ganoids existed in the Silurian times, Dipnoi in the Devonian, Amphibia in the Carboniferous, Reptilia in the Permian, Mammalia in the Trias.
This transitional group of Dipnoi, 'fishes with lungs' but without pentadactyle limbs, is the morphological bridge which joins the Ganoids and the oldest Amphibia.
To what extent the Devonian Ganoids were confined to fresh waters remains yet to be proved; and that many of them lived in the sea is certain.
As compared, therefore, with the Bony fishes, which constitute the great majority of existing forms, the Ganoids form but an extremely small and limited group.
At this period, the bony fishes are not known to have come into existence at all, and the Ganoids held almost undisputed possession of the waters.
The Ganoids of the period are still all provided with unsymmetrical ("heterocercal") tails, and belong principally to such genera as Paloeoniscus and Catopterus.
A sub-order of Ganoids in which the paired fins possess a central lobe.
It seems that this habit was very widespread among the earlier Vertebrates; the larvae of many of the Ganoids and frogs have suctorial disks near the mouth.
Among the paleozoic plated fishes orGanoids the Crossopterygii and the Ctenodipterina (dipneusts) are of great importance.
Part of these Crossopterygii approach very closely in their chief anatomic features to the Dipneusts, and thus represent phylogenetically the transition from the Devonian Ganoids to the earliest air-breathing vertebrates.
Comparative anatomy and ontogeny show clearly that the Ganoids descended from the Selachii, and the Teleostei from the Ganoids.
Some of these fossil Ganoids approach closely to the Selachii; others are nearer to the Dipneusts; others again represent a transition to the Teleostei.
Next to this is the more advanced sub-class of the plated fishes or Ganoids (Figures 2.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "ganoids" in a variety of sentences. We hope that you will now be able to make sentences using this word.
