It is only too clear that the principles as to the modes of mammalian development which can be deduced from the history of the various groups must, for the most part, be stated in a cautious and tentative manner, so as not to give an undue appearance of certainty to preliminary conclusions, which should be held as subject to revision with the advance of knowledge. Much has, however, been already learned, and there is every reason to hope that Experimental Zoölogy and Palæontology, by combining their resources, will eventually shed full light upon a subject of such exceptional difficulty.
FOOTNOTES
[1] Memoirs of the University of California, Vol. I, pp. 209-211.
[2] Voyage of a Naturalist, Amer. ed., pp. 133-134.
[3] J. W. Gregory, The Great Rift Valley, p. 268.
[4] Voyage of a Naturalist, Am. ed., 1891, p. 82.
[5] D. H. Scott, Studies in Fossil Botany, London, 1900, pp. 524-525.
[6] The names, Javan and Sumatran rhinoceroses, are somewhat misleading, since both of these species are also found on the mainland of India.
[7] This plausible and no doubt correct explanation was suggested to me by my colleague, Professor C. F. Brackett.