United States or Czechia ? Vote for the TOP Country of the Week !
Until failing health forbade work with the microscope, he was continually busy with the rational re-grouping of animal forms. They have done more than all else of their period to rationalize the application of our knowledge of the Vertebrata, and have now left their mark for all time on the history of progress, as embodied in our classificatory systems."
These four great branches of the animal world are the vertebrata, mollusca, articulata, and radiata. Comparative anatomy found in Cuvier a student who appreciated its importance and revived its efficiency and honors.
Or among the Teleostei in what respect is the 'Beryx' of the Chalk more embryonic, or less differentiated, than 'Beryx lineatus' of King George's Sound? Or to turn to the higher Vertebrata in what sense are the Liassic Chelonia inferior to those which now exist?
If I had worked my way from a sponge instead of a lobster, I should have found it associated, by like ties, with a great number of other animals into the sub-kingdom 'Protozoa'; if I had selected a fresh-water polype or a coral, the members of what naturalists term the sub-kingdom 'Coelenterata', would have grouped themselves around my type; had a snail been chosen, the inhabitants of all univalve and bivalve, land and water, shells, the lamp shells, the squids, and the sea-mat would have gradually linked themselves on to it as members of the same sub-kingdom of 'Mollusca'; and finally, starting from man, I should have been compelled to admit first, the ape, the rat, the horse, the dog, into the same class; and then the bird, the crocodile, the turtle, the frog, and the fish, into the same sub-kingdom of 'Vertebrata'.
It is impossible for me here to enter on details, but I may specify a few of the points of difference. The crystalline lens in the higher cuttle-fish consists of two parts, placed one behind the other like two lenses, both having a very different structure and disposition to what occurs in the vertebrata.
To these may be added two others not mentioned in the above lists; these are 1, the high pitched voice, which never falls an octave, as does that of the male; and 2, the structure of the generative organs, which in all mammalia more nearly resemble the embryo and the lower vertebrata in the female than in the male.
Finally, with respect to the 'Vertebrata', the same law holds good: certain types, such as those of the ganoid and placoid fishes, having persisted from the palaeozoic epoch to the present time without a greater amount of deviation from the normal standard than that which is seen within the limits of the group as it now exists.
For instance, whether or not there is an open passage from the nostrils to the mouth, the only character, according to Owen, which absolutely distinguishes fishes and reptiles the inflection of the angle of the jaws in Marsupials the manner in which the wings of insects are folded mere colour in certain Algae mere pubescence on parts of the flower in grasses the nature of the dermal covering, as hair or feathers, in the Vertebrata.
Such reptiles as can live in both fresh and salt water, like alligators; and such as are drifted out of the mouths of great rivers on floating trees, as Humboldt says the Orinoco alligators are; might be early colonists. It is manifest, too, that reptiles of other kinds would be among the first vertebrata to people the new continent.
In the vertebrata, we find a brain with a spinal cord, and branching lines of nervous tissue. But here, as in the general structure of animals, the great principle of unity is observed. The brain of the vertebrata is merely an expansion of one of the ganglions of the nervous cord of the mollusca and crustacea.
Word Of The Day