348 VERTEBRATE ZOOLOGY 



or epipubic bones extend forward from the pelvis; the vertebrae are 

 for the most part without epiphyses; the ribs are one-headed, the 

 tuberculum being absent; the mammary glands are modified sweat- 

 glands and are not sebaceous; there is a shallow cloaca; one group 

 (the Echidnidse) has a temporary pouch for incubating the eggs. The 

 oviducts are entirely separate throughout and open by two separate 

 genital pores into the cloaca. 



The majority of these characters hark back to a reptilian ancestry 

 and are therefore to be considered as primitive. It is not believed, 

 however, that the monotremes, as we know them, are at all close to 

 an ideal pro to ty pic mammalian condition; but rather that they are 

 the end-products of a rather highly specialized side line of mammalian 

 evolution, that came off from some early reptilio-mammal stock and 

 that has retained some of the primitive characters of these ancestors. 

 It is not thought, therefore, that the monotremes are in any sense 

 ancestral to the Eutheria. 



Family 1. Echidnidce. This family contains two genera, Echidna 

 and Proechidnd. Echidna aculeata (Fig. 182, D), the " Australian 

 Anteater," is the best known species. It is found in New Guinea, 

 Tasmania and Australia, and several local sub-species are distin- 

 guished. Its characters may be dealt with under two categories: 

 those that are csenogenetic, adaptations for the anteating habit; and 

 those that are palingenetic or primitive. 



Echidna is a typical anteater in all of its adaptations. It has a 

 heavy protective covering of quill-like spines, with an underlying 

 layer of coarse hair. The snout is long and tapering, reminding one 

 rather strongly of a bird's bill. The tongue is extremely long and 

 extensible and is covered with a sticky salivary secretion, which holds 

 the ants when the tongue is thrust into ant holes. The claws are 

 very long and powerful and are used for tearing down ant-hills and 

 for making burrows. As in anteaters of other orders, teeth are lack- 

 ing. Two other characters seem in no way to relate Echidna to the 

 anteating habit; these are first, a rudimentary tail, much like that of 

 a bird, and second, a small spur connected with a peculiar gland on 

 the heel, a structure whose function is not well understood. Of some- 

 what more fundamental importance are the following characters: the 

 cerebral hemispheres are fairly large and well convoluted; there is a 

 temporary marsupial pouch (Fig. 182, C), which seems to -have no 

 relation to the marsupium of the marsupials, but is more nearly 



