United States or Dominica ? Vote for the TOP Country of the Week !
In the same way their affinities are seen to be with the lowest of mammals, the MONOTREMES and MARSUPIALS. The monotremes, such as the duckbill mole and the spiny ant-eater of Australia, reproduce by means of eggs resembling those of reptiles; the marsupials, such as the opossum and the kangaroo, bring forth their young alive, but in a very immature condition, and carry them for some time after birth in the marsupium, a pouch on the ventral side of the body.
In their more advanced mesoderm we find a few contractile longitudinal canals which force the blood through the body by their contractions; these are the first blood-vessels. Transverse section of the branchial gut. A of Balanoglossus, B of Ascidia. r branchial gut, n pharyngeal groove, asterisk ventral folds between the two.
There are also twelve genera of Gasteropods which have yielded 36 species, four of which pass to the Carboniferous group, namely Macrocheilus, Acroculia, Euomphalus, and Murchisonia. Calceola sandalina, Lam. Eifel; also South Devon. a. Ventral valve. b.
With its convex back and its almost flat ventral surface, the creature is like a semi-cylinder in shape, fuller in the hinder portion. On the back, each of the segments, except the last, or anal, segment, puckers into three thick pads, bristling with stiff, tawny hairs.
While the solid, massive bodies of the vertebrae represent the real central axis of the skeleton, the dorsal arches serve to protect the central marrow they enclose. But similar arches develop on the ventral side for the protection of the viscera in the breast and belly. In the higher Vertebrates the majority of these vertebral arches are lost or become rudimentary.
The teats pass into the cavity of a pouch or pocket on the ventral side of the mother, and this is supported by a couple of marsupial bones. The female has three young in the pouch. These Didelphida climb trees like the apes, grasping the branches with their hand-shaped hind feet.
From them has issued the singular organism whose most notable characteristics are as follows: In its general form, the configuration of the head and the great black eyes, the creature, still more than the egg, has the appearance of an extremely minute fish. A simulacrum of a ventral fin increases the resemblance.
Word Of The Day