Now it is a singular fact, first pointed out by Agassiz, that the heterocercal form, which is confined to a small number of genera in the existing creation, is universal in the magnesian limestone, and all the more ancient formations.
Unequal development of the tail lobes of fishes; the possession of a heterocercal tail.
Then the end of the vertebral column turns upward, and strong fin-rays are developed on its ventral side, so that the tail becomes a heterocercal one like that of the less remote ancestors of a later geological period.
The skin generally contains bony elements that are toothlike in structure and often in form; the mouth is usually on the under side of the head, and the tail is nearly always of the heterocercal kind.
Thus as time advanced the heterocercal tail was gradually evolved from the diphycercal, and the homocercal from the heterocercal.
Defn: Unequal development of the tail lobes of fishes; the possession of a heterocercal tail.
It is known as heterocercal, and finally in ordinary fishes the tail becomes homocercal or fan-shaped, although usually some trace of the heterocercal condition is traceable, gradually growing less with the process of development.
Dollo and Boulenger regard the heterocercal tail as a primitive form, the diphycercal form being a result of degradation, connected with its less extensive use as an organ of propulsion.
Boulenger draws a distinction between the protocercal tail, the one primitively straight, and the diphycercal tail modified, like the homocercal tail, from anheterocercal ancestry.
The heterocercal tail is one in which the hindmost vertebrae are bent upwards.
Ryder uses the term heterocercalfor all cases in which any up-bending of the axis takes place, even though it involves the modification of but a single vertebra.
It includes the single family Birkeniidae, characterized by the fusiform body, bluntly rounded head, bilobate, heterocercal tail, and a median row of hooked spinous scales along the ventral margin.
The slender body is covered with small scales and ends in a heterocercal tail.
From the adult forms of Dipnoi we are, however, of opinion that no conclusion can be drawn as to whether their ancestors were provided with a diphycercal or a heterocercalform of caudal fin.
These voracious fishes are characterized by long and slender cylindrical bodies, with enameled scales and mailed heads and heterocercal tail.
The tail is heterocercal and the body covered with rhombic plates.
The caudal part of the fin is at first symmetrical, and the heterocercal tail is produced by the special growth of the ventral part of the fin.
Ganoid-like stage in which there is a true external heterocercal tail.
The notochord in the tail bends slightly upwards, and by the special development of a caudal lobe an externally heterocercal tail like that of Acipenser is established.
The region where they are present soon forms a lobe; and an externally heterocercal tail is produced (fig.
The caudal fin is at first symmetrical, but a special lower lobe grows out and gives to it a heterocercal character.
Now it is a singular fact, first pointed out by Agassiz, that the heterocercal form, which is confined to a small number of genera in the existing creation, is universal in the Magnesian limestone, and all the more ancient formations.
The vertebral centra are usually deeply biconcave, and the tail is of the masked heterocercal type distinguished as homocercal.
The Squalidae have the shape of ordinary fish, the pectoral fins are vertically placed and the body ends in a powerful heterocercal tail.
The vast majority of the Teleostei and some extinct Ganoidei have heterocercal tails of the modified type to which the term =homocercal= is applied.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "heterocercal" in a variety of sentences. We hope that you will now be able to make sentences using this word.
