ANIMALS OF THE LABORATORY DOMAIN. 
No comprehensive study of the animals of the Laboratory domain in 
their relations to its plant life has yet been undertaken, though it can not 
be doubted that this would lead to important results. As has been 
shown in the section on means and agencies of distribution, the inter- 
relations of desert plants and animals are particularly close and varied, 
largely advantageous to both, though often quite the reverse. 
Changes of the flora must react, sometimes directly and manifestly, at 
other times indirectly and obscurely, upon the fauna, and vice versa, but 
the history of these relations has never been followed far in this region. 
A few zoologists who have taken up the study of certain groups of ani- 
mals from an ecological standpoint have made valuable contributions. Of 
these may be specially mentioned the recent studies of reptiles and am- 
phibians by Ruthven (1907). His work, too extended to be reported 
here in detail, includes a discriminating account of the habitat relations 
of the various reptiles and amphibians collected in the vicinity of Tucson. 
The habitats described correspond essentially with those defined in the 
present work, and it is significant that notwithstanding the wide range 
of certain species, as for example some of the bull-snakes, which are 
found from the flood-plain of the Santa Cruz River to the pifion zone 
of the mountains, there is a well-established preference, as a rule, for the 
habitat of some special association of plants. Thus the large lizard 
Sceloporus magister is said to be “common on the greasewood plains’’ and 
also to occur, with the ocotillo and sahuaro, at the foot of the Santa Cata- 
lina and Tucson Mountains, though much less common in these latter 
places; so that its principal habitat in this region is preeminently that 
of the creosote-bush association of plants. Similar notes regarding a large 
percentage of other animals taken in the vicinity of both Tucson and 
Alamogordo indicate that many of them at least exhibit a like habitat 
preference. ‘This is expressed by the author in the general statement 
that each set of environmental conditions which is marked out by a 
distinct plant association has a definite reptile fauna. The summary 
with which the paper closes is of much interest, and some of the general 
statements apply equally to both plant and animal forms; it must be 
said, however, that our present knowledge of the distribution of plants 
on the arid plains by no means warrants, for these, the application of some 
ef the theoretical conclusions of the paper cited. The hypothesis “that 
the reptiles of the arid plains have had their origin in this general region 
(Mexican plateau and proplateau), and that the forms of the pifion-cedar 
and pine-spruce associations have been derived from them”’ would give, 
especially as regards the second proposition, a very inadequate, not to 
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