32 THE DESCENT OF THE PRIMATES 



an extensive scale among their much more 

 numerous Palseozoic ancestors. For the present 

 I hold it to be at the least premature to pin our 

 faith to the one eventuality which those who 

 argue the necessity of an intermediate saurian 

 stage between an amphibian anamniotic ancestor 

 and a mammalian amniotic descendant would 

 wish us to adopt. 



Moreover, as the first steps in the phylogenetic 

 development of amnion and allantois are once 

 for all out of the reach of direct observation, we 

 must be guided solely by speculative argument. 

 And in that case we have a right to exact of those 

 who feel convinced that a megalecithal saurian 

 ancestor comes in somewhere in the pedigree of 

 the placental mammals, that they give us a 

 plausible hypothesis by which we can explain 

 the origin of the amnion. As yet they have 

 utterly failed in this respect, and that most con- 

 scientious and painstaking embryologist, Professor 

 Minot, of Boston, frankly concluded in 1893, that 

 hardly anything " definite is known as to the 

 evolution or phylogenetic origin of the amnion." 



About a year ago a new hypothesis on the 

 origin of the amnion was propounded, ^ in which 



^ A. A. W. Hubreclit, Die Phylogenie des Amnions und die 

 Bedeutung des Trophoblast, Verhandel. Kon, Akademie v. 

 Wetenschappen. Amsterdam, 1895. 



