Insectivora such as moles, shrews and hedgehogs are the hosts of a great variety of species. The same thing may be said of the Rodents, which include porcupines, squirrels, rats, mice and a vast number of other small mammals whose geographical distribution includes almost the whole of the habitable globe. Probably more different species of fleas have been collected from Insectivora and Rodents than from all the other orders of mammals grouped together. The Carnivora, excluding the Pinnepedia, or seals, sea-lions and walruses, harbour numerous species. Among the Edentata a very remarkable and highly specialised genus of fleas is parasitic on armadilloes in South America. This genus (_Malacopsylla_) consists of two species only, which are confined to South America and are found on the armadilloes and on carnivorous animals which probably have preyed on them. The thorax of these fleas is much reduced and very small in size. Their piercing organs are slender and weak, but they possess enormous spines on the legs with which they hold on to their hosts. These two South American fleas (_M. grossiventris_ and _M. androcli_) will be referred to again later as striking examples of fleas with strongly developed legs and weakly constructed mouth-parts. The contrary combination of powerful mouths and degenerate legs is also found in other groups of fleas, as will be seen in the chapter on the chigoes. The Marsupials of Australia and South America have special fleas which were probably associated with this strange order of pouched mammals before they became divided into the American and Australian groups. Fleas have been collected on the spiny ant-eater (_Echidna_) which belongs to the lowest order of Monotremes or egg-laying mammals. On almost every form of bird, including the most aquatic kinds, fleas of various species have been obtained. Only one instance has been recorded of a flea occurring on a reptile. A female of one of the species of burrowing chigoes (_Echidnophaga ambulans_) from Australia was collected by Dr Woodward from the Brown Snake (_Diemenia superciliosa_). This reptile, which is well known in Australia, belongs to a sub-family that contains some of the most deadly poisonous snakes and is allied to the cobras. The Brown Snake is a terrestrial snake, and one must regard the presence of the flea on such a host as a rare and chance occurrence. The snake was captured at Herdman’s Lake, near Perth in West Australia. The same species of flea has also been obtained from the phalangers (_Trichosurus_) which live in the tops of the Australian gum-trees; from the little terrestrial and nocturnal rat kangaroos (_Bettongia_); and from the banded ant-eater (_Myrmecobius_), another Australian Marsupial. It is possible that the flea moved from some small mammal which was being devoured by the snake and managed to fix itself between the scaly plates of the reptile.