United States or Côte d'Ivoire ? Vote for the TOP Country of the Week !
We have seen that birds and reptiles were once intimately connected together; and the Monotremata now connect mammals with reptiles in a slight degree. But no one can at present say by what line of descent the three higher and related classes, namely, mammals, birds, and reptiles, were derived from the two lower vertebrate classes, namely, amphibians and fishes.
The Monotremata are eminently interesting, as leading in several important points of structure towards the class of reptiles. In attempting to trace the genealogy of the Mammalia, and therefore of man, lower down in the series, we become involved in greater and greater obscurity; but as a most capable judge, Mr.
The Marsupials differ from the Monotremata by possessing nipples; so that probably these organs were first acquired by the Marsupials, after they had diverged from, and risen above, the Monotremata, and were then transmitted to the placental mammals. Prof. See, also, a memoir by Dr. Max Huss, on the mammary glands, ibid. How then are we to account for male mammals possessing mammae?
The Monotremata have the proper milk-secreting glands with orifices, but no nipples; and as these animals stand at the very base of the mammalian series, it is probable that the progenitors of the class also had milk-secreting glands, but no nipples.
It is well known that none above the marsupialia, or pouched animals, are native to it. The most conspicuous are these marsupials, which exist in great varieties here, though unknown in the elder continent, and only found in a few mean forms in America. Next to them are the monotremata, which are entirely peculiar to this portion of the earth.
One of these he devotes to man; in another he places both the marsupials and the Monotremata; so that he makes man as distinct from all other mammals as are these two latter groups conjoined. This view has not been accepted, as far as I am aware, by any naturalist capable of forming an independent judgment, and therefore need not here be further considered.
Nightjars, noise made by some male, with their wings; elongated feathers in. Nilghau, sexual differences of colour in the. Nilsson, Prof., on the resemblance of stone arrow-heads from various places; on the development of the horns of the reindeer. Nipples, absence of, in Monotremata. Nitsche, Dr., ear of foetal orang. Nitzsch, C.L., on the down of birds. Noctuae, brightly-coloured beneath.
To what point of the Palaeozoic epoch, then, must we, upon any rational estimate, relegate the origin of the Monotremata? The investigation of the occurrence of the classes and of the orders of the Sauropsida in time points in exactly the same direction.
At the epoch of the Trias, therefore, the Marsupialia must have already existed long enough to have become differentiated into carnivorous and herbivorous forms. But the Monotremata are lower forms than the Didelphia which last are intercalary between the Ornithodelphia and the Monodelphia.
To what point of the Palaeozoic epoch, then, must we, upon any rational estimate, relegate the origin of the Monotremata? The investigation of the occurrence of the classes and of the orders of the Sauropsida in time points in exactly the same direction.
Word Of The Day