In summer the nest-chamber of the females, which is distinct from the summer-burrow of the males and is furnished with one exit and several entrances, is carefully lined with hay. Towards the end of April the males visit the females in their own apartments; and four or five weeks later the first litter of blind and naked young--varying in number from half a dozen to eighteen--is produced. These rapidly develop their fur, and open their eyes about the eighth or ninth day; and within a fortnight are driven away from the parental burrow to construct a new one of their own. Freed from one family, the old hamsters set about producing a second one, which usually comes into the world in July. The annual increase is, however, by no means limited to the older individuals, for the members of the early spring litter are able to produce young ones in the autumn. Hamsters frequently make their appearance in enormous swarms, when they do vast damage to crops. In return, the winter granaries of these rodents are frequently raided by the peasants of countries where they are common; the flesh of the hamster is also eaten, and its fur employed for lining cloaks and coats. THE DUCKBILL OR PLATYPUS (_Ornithorhynchus anatinus_) For many years it was reported by the natives of Australia that the extraordinary warm-blooded quadruped known to naturalists as the duckbill, or platypus, produced its young from eggs laid in a burrow by the female. That a mammal--and a mammal, although of an altogether peculiar and out of the way type, the creature undoubtedly is--should lay eggs was, however, too much for the minds of stay-at-home naturalists, and the fiat accordingly went forth that the native story was to be discredited. And discredited it therefore was. In nature, as in other things, truth will, however, ultimately prevail; and we now know for certain that the female lays in a burrow in the bank of some river or pool a couple of hard-shelled, oval eggs, which in due course hatch out into naked, helpless young, furnished with soft sucking lips. Not that they suck in the ordinary mammalian fashion, for the female platypus has no nipples, but her milk oozes out in the breast from a number of sieve-like pores, from the surface of which it is sucked up by her offspring. Such a difference from the ordinary mammalian way of doing business proclaims the wide distinction between the platypus, and, it may be added, its relatives the spiny ant-eaters or echidnas (one of which forms the subject of another illustration), and all other warm-blooded quadrupeds. Nor is this all, for in the structure of their skeleton and soft internal parts the platypus and the echidna display many marks of affinity with reptiles and birds, which are totally wanting in other mammals. These two creatures represent indeed a group by themselves, so that mammals may be divided into two great primary sections, the one embracing only the two egg-laying types, and the other all the rest.