No. 397.] ZOOLOGY OF THE HORN EXPEDITION. 27 
face adapted to prevent the evaporation of moisture, and their 
seeds can survive a long exposure, but germinate very rapidly 
as soon as the moist season arrives. The animals are such as 
can travel long distances with ease, like the dingo and the 
kangaroo, or can subsist on the dews of early morning. Some, 
like the burrowing frogs and mollusks, hide away from the 
withering sun, and others produce eggs which will not develop : 
until after the mud in which they have been deposited dries up. 
Professor Spencer thinks there is little attempt at protective 
coloration, in the struggle for existence, except in a general way. 
Nature seems to devote all her energies to the production of 
eggs which will develop precociously. The young, especially of 
insects, seem impelled to feed ravenously, and reach maturity 
before the favorable season is past. 
As a result of the variable seasons, many species show a con- 
siderable discrepancy in size, individuals reared in successive 
good seasons being unusually large, while those growing in a 
succession of poor seasons are small. In one species, Phasco- . 
logale cristicauda, the length of the head and body of the small- 
est adult male was 136 mm.; of the largest, 220 mm. The 
relationship of the fauna of the center to that of the surround- 
ing regions is one of the strongest points in determining the 
probable source of Australian marsupials. The author divides 
the twenty-four species of the center into three main groups : 
1. Those of continental distribution: Trichosurus vulpecula, 
Sminthopsis murina, S. crassicaudata, Perameles obesula. 
2. A larger number, characteristic of the inland portion of 
eastern Australia, and of the south and west: Macropus robu- 
stus, M. rufus, Petrogale lateralis, Onychogale lunata, Lagorche- 
stes conspicilatus, var. leichardtit, Bettongia lesueuri, Cheropus 
castanotis, Phascologale calura, P. cristicauda, Dasyurus geof- 
froyii, Antechonomys laniger, Myrmecobius fasciatus. 
3. Those which as far as now known are peculiar to the 
central region : Peragale minor, P. leucura (probably), Perameles 
eremiana, Sminthopsis psammophilus, S. larapinta, Phascologale 
macdonnallensis; Dasyuroides byrnei, Notoryctes typhlops. 
Professor Spencer calls attention to the fact that there is no 
indication of primitive monotremes of marsupials characteristic 
