^be )Egg»%a^inQ flibammals. 



FIFTEENTH ORDER: Monotremata 



lOR a long time the point 

 has been eagerly argued, 

 as to the order in which 

 the Monotremes or Egg- 

 laying Mammals ought to 

 be placed; but now this 

 question has been settled. 

 The opinion of older zo- 

 ologists, who saw a dis- 

 tinct class of the animal 

 world in the Monotremes, 

 had certainly, temporarily 

 at least, lost its sway, yet 

 it has now partly regained 

 it, and no zoologist of the present time places the 

 Duck-mole and the Echidna (both of which might 

 justly be regarded as representing distinct sub- 

 classes among mammals) among the pouched ani- 

 mals, or still less among the edentates. 

 Physical Peculiar- That the Monotremes really suckle 

 ties of the Mono- their young has long been estab- 

 tremes. lished beyond a doubt; yet the close 



investigations of Gegenbaur were necessary to ac- 

 quaint us with the true nature of the organs of lacta- 

 tion. The glands, which are situated on the sides 

 of the abdomen, open in many fine ducts of the 

 skin, which in these places is covered with hair. 

 As many male mammals have similar glands in 

 the same places, the first dissectors did not take 

 these to be real organs of lactation until Meckel 

 proved that these glands were not developed in the 

 male Duck-mole, and Baer noticed that the lacteal 

 glands of Whales were similarly constructed. Owen 

 examined the glands in 1832 and found each to have 

 about one hundred and twenty openings in the skin, 

 secreting a nutritive fluid, which he found in the 

 stomach of the young in a coagulated state. There- 

 fore he classified the Monotremes among the mam- 

 mals. But on the second of September, 1884, 

 Haacke reported to the Royal Society of South 

 Australia, in Adelaide, that- he had a few weeks pre- 

 viously found an egg, which he produced at the 

 meeting, in a so far unknown brooding pouch of a 

 living Echidna, and on the same day a cablegram 

 was read in Montreal, which informed the assembled 

 members of the British Association that another 

 naturalist, Caldwell, who was at that very time work- 

 ing in Australia, had found that the Monotremes/ 

 lay eggs. These discoveries again rendered the 

 closer relation of the Monotremes to other mammals 

 more questionable, the more so, as Gegenbaur proved, 

 in 1886, that the glands which furnish nourishment 

 to the young do not correspond in their structure 

 with the sebaceous glands, as do the lacteal glands 

 of all other mammals, but represent modified sweat- 



glands. If pne further considers that, according to 



the discovery made by Thomas as late as 1888, the 

 Duck-mole has, during a considerable time of its life, 

 teeth, which are true teeth but differ greatly from 

 those of any other living mammal, and that the 

 blood-heat of the Monotremes amounts to twenty- 

 eight degrees Celsius (sixty degrees Fahrenheit) at 

 the most, differing in this from all other warm- 

 blooded animals, one would think the action justified 

 if we were to separate the Monotremes as a second 

 main division of mammals from the first, in which 

 arrangement we would classify the pouched ani- 

 mals and higher Mammalia as genuine mammals; or 

 it would not be erroneous even it we were to place 

 them as a distinct class among the vertebrates. 

 Such a division will perhaps be decided on finally; 

 but up to the present we classify these animals as 

 the last and lowest order of mammals, composed 

 only of themselves. 



The Monotremes have an outer envelope of skin 

 similar to that of other mammals. The Duck-mole 

 is clothed in fur and the Echidna has its covering of 

 spines and bristles; but in other respects they differ 

 markedly from the other known forms of the class 

 in external appearance as well as internal structure. 

 A hard beak, similar to that of an aquatic bird, 

 stands them in stead of a mouth, and the intestines, 

 the urinary and genital organs all terminate in one 

 orifice, the so-called "cloacal aperture." This is 

 a formation we find again in the birds, which the 

 Monotremes also resemble by reason of their large- 

 yolked eggs, the possession of a single forked ster- 

 nal bone, formed by the two ankylosed or conjoined 

 collar bones or clavicles, and the partially developed 

 condition of the right ovary. While for these rea- 

 sons their relation to both birds and reptiles can 

 not be denied, they exhibit an affinity also to the 

 pouched animals by reason of their possession of 

 marsupial bones. 



The Monotremes are small mammals, with a 

 sturdy, somewhat flattened body, very short legs, 

 beak-shaped -jaws covered with a -dry skin, small 

 eyes, a short tail, feet placed at a diverging angle 

 in regard to one another, armed with strong claws 

 and a hollow spur upon the heel of the male, 

 this spur communicating with a special secretory 

 gland. The outer ear-conch is absent; teeth exist 

 only in the Duck-mole and consist of flat, disk-like, 

 laminse or "plates" furnished with tubercles or cusps 

 along the edges of their upper surfaces, and articu- 

 lated loosely superficially with the jawbone, rather 

 than having inserted roots. 



Besides the bones of an extinct Echidna, teeth of 

 prehistoric animals, similar to those of the Duck- 

 mole have been found; but at present this peculiar 

 order is limited to the two families of the Echidni- 

 dae and the Duck-moles. 



(595) 



