104 GENERAL EVOLUTION". 



gresses chiefly during the later periods of embryonic life, and is 

 therefore a "developmental character." Owen has endeavored to 

 distinguish the j)rimary divisions of Mammalia by the character 

 of these convolutions, whereas they really define only the sub- 

 groups of the orders. For we have Lissencephalous (smooth- 

 brained) monkeys — certain lemurs — and smooth-brained Eumi- 

 nants — i. e., the extinct Brachyodon and Anoplotherium, accord- 

 ing to Lartet and Gratiolet. The lowest types of the existing 

 smooth-brained Mammalia, including especially those with no 

 or rudimental corpus callosum, the Marsupials, are also distin- 

 guished by the non-development of the deciduous teeth * (except- 

 ing one jiremolar). If now, through some toj)ographical change, 

 the whole series of Mammalia between the smooth-brained and 

 convolute-brained were lost to us, as by the elevation of a region, 

 and the absence of favorable localities or bodies of water for the 

 preservation of their remains, we would have to study two homol- 

 ogous groups, with the heterologous terms of each corresponding 

 with each other, as do now the genera of the Clamatores and Os- 

 cines of the Arcifera and Eaniforraia, etc. 



In the same way the characters defining Implacental Mam- 

 malia will be found transitional in some type, and this great se- 

 ries, homologous with the Placentals, will have to be placed in 

 closer connection, in its genera, with the series of the latter, with 

 genera of the same, perhaps, now extinct. 



y. Of Mimetic Analogy. 



It has been often remarked that the animals of the Equatorial 

 Ethiopian region were very generally of smoky and black colors. 

 This is remarkably the case, and the peculiarity of the genus Homo 

 in this respect is shared by birds, reptiles, and fishes in a consider- 

 able degree. This can not be traced to the effect of torrid climate, 

 for the same latitudes in India and the Malaysian Archipelago, 

 and in South America, do not produce such colors. 



The similarity in color of desert types has also been remarked. 

 The gray sand-hue so well adapted for concealment is universal, 

 with few variations, in the reptiles of the Tartar and Arabian 



* This I have alluded to as the non-development of the permanent series ; the 

 homology of the dental system of Marsupials appears, however, to be with the latter 

 and not with the milk series. See "Flower," " Trans. Roy. Soc.," 1867. (Wortman 

 now denies the correctness of Flower's view, and demonstrates that the milk series 

 is primitive. See "Encyclopaedia of Dentistry," 1886. Ed. 1886.) 



