160 The Outline of Science 



and is normally concealed beneath the flesh, but in the embryo the 

 tail projects freely and is movable. Up to the sixth month of 

 the ante-natal sleep the body is covered, all but the palms and 

 soles, with longish hair (the lanugo), which usually disappears 

 before birth. This is a stage in the normal development, which 

 is reasonably interpreted as a recapitulation of a stage in the 

 racial evolution. We draw this inference when we find that the 

 unborn offspring of an almost hairless whale has an abundant 

 representation of hairs; we must draw a similar inference in 

 the case of man. 



It must be noticed that there are two serious errors in the 

 careless statement often made that man in his development is 

 at one time like a little fish, at a later stage like a little reptile, at 

 a later stage like a little primitive mammal, and eventually like 

 a little monkey. The first error here is that the comparison 

 should be made with embryo-fish, embryo-reptile, embryo-mam- 

 ma.}, and so on. It is in the making of the embryos that the great 

 resemblance lies. When the human embryo shows the laying 

 down of the essential vertebrate characters, such as brain and 

 spinal cord, then it is closely comparable to the embryo of a lower 

 vertebrate at a similar stage. When, at a subsequent stage, its 

 heart, for instance, is about to become a four-chambered mamma- 

 lian heart, it is closely comparable to the heart of, let us say, a 

 turtle, which never becomes more than three-chambered. The 

 point is that in the making of the organs of the body, say brain 

 and kidneys, the embryo of man pursues a path closely corre- 

 sponding to the path followed by the embryos of other backboned 

 animals lower in the scale, but at successive stages it parts com- 

 pany with these, with the lowest first and so on in succession. A 

 human embryo is never like a little reptile, but the developing 

 organs pass through stages which very closely resemble the corre- 

 sponding stages in lower types which are in a general way 

 ancestral. 



The second error is that every kind of animal, man included, 



