368 CHAPTERS ON THE NATURAL HISTORY 



Opossum (D. derbiana) typifies this group, the third one having 

 been named Micoureus (or Grymceomys of Burmeisterj, it "differ- 

 ing only from Metachirus by the comparatively smaller size of 

 its members and by certain slight differences in the shape of 

 their teeth. Its best known species is the Murine opossum (I), 

 murina), no larger than a house-mouse, of a bright-red color, 

 which is found as far north as central Mexico, and extends 

 thence right down to the south of Brazil. The last subgenus 

 contains three or four wonderfully shrew-like species, of very 

 small size, with short, hairy, and non-prehensile tails, not half 

 the length of the trunk, and with wholly unridged skulls. The 

 most striking member of this group is the Three-striped opos- 

 sum (IK tristriata), from Brazil, which is of a reddish-gray col- 

 or, with three clearly defined deep-black bands down its back, 

 very much as in some of the striped mice of Africa. This sub- 

 genus has been named Hemiurus or "half-tail'' by Geoffroy 

 Saint-Hilaire (Microdelphys of Burmeister), and should perhaps 

 be allowed full generic rank." 



Very considerable attention has been paid to the anatomy of 

 the Didelphyidce, and some of this is from the pens of American 

 writers; still the subject has by no means been exhausted, and 

 good contributions to it are still in order, and will be highly ap- 

 preciated by science, come from what quarter they may. Espe- 

 cially is it to be desired that the morphology of the young of this 

 family be thoroughly worked out, giving the various stages of 

 development from the time of conception to the time of subadult 

 life. 



In speaking in a general way of the anatomy of the Marsu- 

 pialia, Sir William Henry Flower, now in charge of the Nat- 

 ural History Departments of the British Museum, has said 

 the " mammae vary much in number, but are always abdom- 

 inal in position, have long teats, and in most of the species 

 are more or less enclosed in a fold of the integument, 

 forming a pouch or marsupium. though in some this is entirely 

 wanting, and the newly-born, blind, naked, and helpless young, 

 attached by their mouths to the teat, are merely concealed and 

 protected by the hairy covering of the mother's abdomen. In 

 this stage of their existence they are fed by milk injected into 

 their stomach by the contraction of the muscles covering the 

 mamillary gland, the respiratory organs being modified tempor- 

 arily, much as they are permanently in the Cctacea, — the elonga- 



