Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: July 27, 2025
When we pass on to the fishes, we find their intelligence remaining at a very low level. We do not see any material advance in mental development until we go on to the Amphibia and Reptiles. There is still greater advance when we come to the Mammals, though even here the minds of the Monotremes and of the stupid Marsupials remain at a low stage.
On the other hand, the Crossopterygian Ganoids exhibit the closest connection with Lepidosiren, and thereby with the Amphibia. It should not be forgotten that the development of the Lampreys exhibits curious points of resemblance with that of the Amphibia, which are absent in the Sharks and Rays.
It is a fair inference that the tadpole stage in the life history of the frog represents a stage in the evolution of its kind, that the Amphibia are derived from fishlike ancestral forms. This inference is amply confirmed in the geological record; fishes appeared before Amphibia and were connected with them by transitional forms.
From the Dipneusts upwards we now trace a progressive development of the vascular system, which ends finally with the loss of branchial respiration and a complete separation of the two halves of the circulation. In the Amphibia the partition between the two auricles is complete.
During the dry season they bury themselves in the dry mud, and breathe the atmosphere through lungs, like the amphibia and the higher vertebrates. In this double respiration they resemble the lower amphibia, and have the same characteristic formation of the heart; in this they are much superior to the fishes.
Morgan evidently does not realise that the Birds and Reptiles must have been derived from Amphibia, and that the embryo Reptile or Bird with gill slits and gill arches is merely a tadpole enclosed in an egg shell. The Frog in its adult state differs much from a Fish, while the larva in its gill arches and gill slits resembles a Fish.
Indeed, as we trace back the still earlier history, more and more characters are found which are the common properties of wider and wider arrays of organisms, for at one time the embryo exhibits gill-slits in the sides of its throat which in all essential respects are just like those of the embryos of birds and reptiles and amphibia, as well as of other embryo mammals and these gill-slits are furthermore like those of the fishes which use them throughout life.
But some of the tailed Amphibia the salamanders remain entirely in the water when they are young, and afterwards spend most of their time on land. In the adult state they only breathe air through lungs. In the centre a yelk-sac still hangs from the gut. The external gills are gracefully ramified.
It is true that the Amphibia have two lungs, right and left. Ventral and pectoral walls are removed. The greater part of the body-cavity is taken up with the liver, from the middle part of which the caecum and the vermiform appendix protrude. Immediately behind the single structure of the thyroid gland a median groove, the rudiment of the trachea, is detached from the gullet.
Word Of The Day
Others Looking