. Evidence as to man's place in nature . eaves the organ in which it is formed in a simi-lar fashion and enters the organic chamber prepared for itsreception in the same way, the conditions of its developmentbeing in all respects the same. It has not yet been possible(and only by some rare chance can it ever be possible) tostudy the human ovum in so early a developmental stage asthat of yelk division, but there is every reason to concludethat the changes it undergoes are identical with those ex-hibited by the ova of other vertebrated animals; for theformative materials of which the rudimentary
. Evidence as to man's place in nature . eaves the organ in which it is formed in a simi-lar fashion and enters the organic chamber prepared for itsreception in the same way, the conditions of its developmentbeing in all respects the same. It has not yet been possible(and only by some rare chance can it ever be possible) tostudy the human ovum in so early a developmental stage asthat of yelk division, but there is every reason to concludethat the changes it undergoes are identical with those ex-hibited by the ova of other vertebrated animals; for theformative materials of which the rudimentary human bodyis composed, in the earliest conditions in which it has beenobserved, are the same as those of other animals. Some ofthese earliest stages are figured below and, as will be seen, theyare strictly comparable to the very early stages of the Dog;the marvellous correspondence between the two which is keptup, even for some time, as development advances, becomingapparent by the simple comparison of the figures with thoseon page Fig. 15—A. Hitman ovum (after KoUiker). a. germinal vesicle, b. germinalspot. B, A very early condition of Man, with yelk-sac, allantois and amnion (original). C. A more advanced stage (after Kolliker), compare fig. 14, C. Indeed, it is very long before the body of the young humanbeing can be readily discriminated from that of the young 67 puppy; butj at a tolerably early period, the two become dis -tinguisbable by the different form of their adjuncts^ the yelk-sac and the allantois- The former^ in the Dog^ becomes longand spindle-shaped, while in Man it remains spherical: thelatter, in the Dog, attains an extremely large size, and thevascular processes which are developed from it and eventuallygive rise to the formation of the placenta (taking root, as itwere, in the parental organism, so as to draw nourishmenttherefrom, as the root of a tree extracts it from the soil) arearranged in an encircling zone, vrhile in Man, the allantoisremains co
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