ii2 THE KINGDOM OF MAN 



Australian land surface. This connection is suggested 

 by the discovery in the Santa Cruz strata, considered 

 to be of early Tertiary date, of remains of a huge horned 

 tortoise which is generically identical with one found 

 fossil in the Australian area of later date, and known 

 as Miolania. In the same wonderful area we have the 

 discovery in a cave of the fresh bones, hairy skin, and 

 dung of animals supposed to be extinct, viz., the giant 

 sloth, Mylodon, and the peculiar horse, Onohippidium. 

 These remains seem to belong to survivors from the last 

 submergence of this strangely mobile land-surface, and 

 it is not improbable that some individuals of this ' ex- 

 tinct ' fauna are still living in Patagonia. The region is 

 still unexplored and those who set out to examine it have, 

 by some strange fatality, hitherto failed to carry out 

 the professed purpose of their expeditions. 



I cannot quit this immense field of gathered fact and 

 growing generalisation without alluding to the study of 

 animal embryology and the germ-layer theory, which 

 has to some extent been superseded by the study of 

 embryonic cell-lineage, so well pursued by some Amer- 

 ican microscopists. The great generalisation of the 

 study of the germ-layers and their formation seems to 

 be now firmly established namely, that the earliest 

 multicellular animals were possessed of one structural 

 cavity, the enteron, surrounded by a double layer of 

 cells, the ectoderm and endoderm. These Enter ocala 

 or Ccelentera gave rise to forms having a second great 

 body-cavity, the crelom, which originated not as a split 

 between the two layers, as was supposed twenty-five years 

 ago by Haeckel and Gegenbaur and their pupils, but by 

 a pouching of the enteron to form one or more cavities 

 in which the reproductive cells should develop pouch- 

 ings which became nipped off from the cavity of their 



