GROUPS OF MAMMALS. 241 



running 1 through a passage-way of two or three feet in length, 

 the nest itself is found. It is in a pocket-like excavation, and 

 a circular section is cut out of the front of the bank so as to 

 make an opening through which the nest can be seen. The 

 nest is lined with dead leaves, in which lies an opossum curled 

 up and sound asleep. At the back of the case a sectional view 

 of the bank is represented, and by means of an opening cut 

 here and there, the course of the burrow is plainly seen. In 

 the foreground is an old mother opossum Avith several young 

 ones riding on her back, clinging to her gray coat, while the 

 head of another protrudes from her pouch. This represents 

 the manner in which the opossum carries her young after they 

 have reached a certain age. From a small branch hangs an- 

 other opossum, suspended by its prehensile tail, sprawling in 

 mid-air. This specimen is a female, and shows the size and 

 location of the wonderful marsupial pouch. Another individual 

 is climbing up the trunk of the tree. A fourth specimen, 

 which has been disturbed by another, is pausing to protest 

 with widely opened mouth, while in the act of creeping into 

 the mouth of the burrow. 



Please notice the number of facts that are taught by this 

 simple little group. It shows that the opossum is a marsu- 

 pial, and the female carries her young in a pouch in her own 

 body j that when the young reach a certain age, they ride upon 

 the mother's back, clinging to her fur ; that the animal is ar- 

 boreal in habit, and has a prehensile tail, by which it is capable 

 of suspending itself ; that it burrows in banks in dry situations, 

 and sleeps curled up like a ball in a bed of dry leaves. It also 

 shows the full size of the adult, the young of the previous year, 

 and the recent brood. But for an unfortunate accident, which 

 has yet to be. repaired, it would also show the number born at 

 one birth. Of course in this group the grass and moss is 

 properly represented, and there are artificial leaves on the tree 

 branches which enter the group. 



Groups of this class can easily be made to show the ordinary 

 nesting and breeding habits of the animals represented. Now 

 it happens that animals of some species make a variety of nests, 

 according to circumstances or caprice. In 1889 we prepared a 

 group in three sections, each of which shows one of the habits of 

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