GENESIS OF MAN. 43 



is gradually absorbed and appropriated by the embryo, and fur- 

 nishes a portion of its nutrition. Simultaneously with the amnion 

 is developed also another important organ, the Allantdis, or pri- 

 mordial urinary sack. Both these organs are confined to the three 

 highest classes of Vertebrates (reptiles, birds and mammals). The 

 embryo now begins to manifest decided mammalian characteristics. 

 Already, the gills have disappeared, having become transformed 

 into jaws, hyoid bones, and otolithes : the heart has acquired its 

 four chambers, and the swim-bladders have been specialized into 

 lungs. For a while the uro-genital and excrementary orifices 

 empty into the common cloaca giving it the monotrcme character. 

 Then, while the allantois is still present, a partition separates 

 these, making both open externally. This is the Marsupial stage. 

 Lastly, the allantois is transformed into a placenta, and the pure 

 mammalian stage is reached. Leaving the great branches of the 

 Carnivora and Rodentia on the one hand, and of the Ungulata and 

 Cetacea on the other, the embryo now passes through the various 

 phases of a Sloth-form, an Ape-form, and an Anthropoid-form ; 

 and, conditions being normal, emerges on the two hundred and 

 eightieth day of gestation with the form of a human being. 



No one who experiences the least regard for natural truth, what- 

 ever views he may hold respecting the meaning of particular facts, 

 can contemplate so remarkable a series of phenomena as this, and 

 realize that he has himself once been the subject of such a strange 

 course of development, without being led into a train of reflection 

 which will open up to his mind broader and juster conceptions of 

 the universe. 



At the same time it would be impossible to exaggerate the 

 degree of added strength which a popular acquaintance with the 

 bare facts of ontogenesis would impart to the hypothesis of devel- 

 opment or modern doctrine of descent, and thus indirectly to the 

 general conception of the law of universal evolution. 



III. 



PHYLOGENESIS. 



THE fundamental biogenetic law that ontogenesis is an abridged 

 repetition of phylogenesis, that the transformations through 

 which the individual passes during its ante-natal and post-natal ex- 

 istence in the brief period of its career, are a mere reflection of those 



