52 Dynamic Theory. 



dyles and bones indicates the state of development of their owner. 



It has been held that the valves in the portal veins which exist in 

 certain animals, do not exist in man but Dr. Bryant, of Worcester, 

 Mass. , has discovered that they do exist in the portal veins of infants 

 a few weeks old, and disappear in the adult. (The portal veins convey 

 the black blood from the intestines and the liver. ) 



Every other animal race as well as the human, has its rudimentary or 

 atrophied organs. Those of the higher apes are mostly identical with 

 ours. But in those branches of the animal kingdom that are not in 

 our line or very nearly related to us, they are, of course, different. 

 These atrophied organs are often useful in tracing the pedigree of the 

 animal to which the}^ belong. Thus the frog has on his hind limb, five 

 digits. But on his fore limb he shows only four. He has, however, 

 the other in suppressed form, concealed under the skin. The embryo 

 of the whale has bony teeth, but when it grows up it has only the whale- 

 bone or baleen, the teeth being absorbed and never cutting the gums. 

 The Deductor or Caing whale has from nine to thirteen teeth on each 

 side, above and below, but loses them all with age. Some of the dol- 

 phin whales have teeth which they lose young, others have teeth which 

 never cut the gum. The armadillo belongs to the edentates, or so called 

 toothless tribes, which have, however, back teeth but no front ones. 

 Its first teeth are covered with enamel like those of the higher mammals. 

 These are lost, and behind them come up the permanent ones without 

 enamel. Behind the primitive ^eeth are small sacs which correspond 

 with the germs of the permanent teeth of the higher mammalia. (Baird's 

 Annual 1874 289.) The above facts indicate that the whale has de- 

 scended from a land mammal, and the armadillo from a diphyodont 

 mammal stock, and the frog from a five-fingered, tailed amphibian. 



The monotremes, ornithorhynchus and echidna are a sort of cross 

 between birds and mammals. They have bodies like rats, and they 

 suckle their young through pores in the skin leading into the milk 

 glands, but they are destitute of nipples. Like birds they have no ex- 

 ternal organs of generation, and are furnished with a cloaca or common 

 passage as exit for all excrementitious matters. (See fig. 30. ) When 

 young, the sexes are indistinguishable, both being alike even to the 

 spurs which sprout on the hind leg of each. But in the course of 

 growth, the spur on the female is suppressed while the male spur is 

 fully developed like that of a rooster, and this constitutes the only sex- 

 ual mark. They have a bill like that of a duck, and their feet are 

 both clawed and webbed. 



All the lower animals also pass, in their embryonic life, through 

 stages of development corresponding to the permanent conditions of 

 their predecessors. For example, the white fish when young bears a 



