. Man's place in nature, and other anthropological essays. evel-opment which are exhibited by a Dog, for example, are now as wellknown to the embryologist as are the steps of the metamorphosisof the silk-worm moth to the school-boy. It will be useful to con-sider with attention the nature and the order of the stages of caninedevelopment, as an example of the process in the higher animalsgenerally. 48 MANS PLACE IN NATURE The dog, like all animals, save the very lowest (and further in-quiries may not improbably remove the apparent exception), com-mences its existence as an egg: as a body which
. Man's place in nature, and other anthropological essays. evel-opment which are exhibited by a Dog, for example, are now as wellknown to the embryologist as are the steps of the metamorphosisof the silk-worm moth to the school-boy. It will be useful to con-sider with attention the nature and the order of the stages of caninedevelopment, as an example of the process in the higher animalsgenerally. 48 MANS PLACE IN NATURE The dog, like all animals, save the very lowest (and further in-quiries may not improbably remove the apparent exception), com-mences its existence as an egg: as a body which is, in every sense,as much an egg as that of a hen, but is devoid of that accumulationof nutritive matter which confers upon the birds egg its excep-tional size and domestic utility; and wants the shell, which wouldnot only be useless to an animal incubated within the body of itsparent, but would cut it off from access to the source of that nutri-ment which the young creature requires, but which the minute eggof the mammal does not contain within Fig. 13.—A. Egg of the Dog, with the vitelline membrane burst, soas to give exit to the yelk, the germinal vesicle (a), and its includedspot (&). B. C. D. E. F. Successive changes of the yelk indicated in thetext. After Bischoff. The Dogs egg is, in fact, a little spheroidal bag (Fig. 13),formed of a delicate transparent membrane called the vitellinemembrane^, and about -rioth to rroth of an inch in diameter. Itcontains a mass of viscid nutritive matter — the yelh — withinwhich is enclosed a second much more delicate spheroidal bag,called the germinal vesicle (a). In this, lastly, lies a more solidrounded body, termed the germinal spot (b). The egg, or Ovum, is originally formed within a gland, fromwhich, in due season, it becomes detached, and passes into the liv-ing chamber j&tted for its protection and maintenance during theprotracted process of gestation. Here, when subjected to the re-quired conditions, this minute
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