68 THE WAY LIFE BEGINS 



rated, with increasing divergences in different animals in the 

 case of the vascular, respiratory, muscular, and nervous 

 systems. 



It is, in fact, a law of the development of organisms that 

 the peculiarities which distinguish groups of animals — those, 

 for example, that separate the rabbit from man — only appear 

 gradually. The closer the resemblance or relationship, the 

 later these differences appear. 



Compare, for the illustration of this law, the appearance of 

 the human embryo of twenty-one days with that of the 

 rabbit only a few days old. (Figure 9.) Their sizes are prac- 

 tically the same, being about two-tenths of an inch long. Both 

 show the gill clefts, which are expressions of nature's inability 

 to forget that man and all the vertebrates were once fish; 

 the two higher sense organs, the eye and the ear, are marked 

 out, but there is no trace of limbs. 



By the twenty-eighth day the human embryo is almost 

 half an inch long, and the rabbit within two days of birth. 

 Comparing, however, similar stages, there is little difference 

 between them. The head and its various parts are clearly 

 marked out, and the rudiments of the eye, ear and limbs are 

 seen. The head bends almost at right angles to the body. 

 The tail of the human embryo is twice as long as the legs. 

 Inside of the body, all of the principal organs are outlined. 

 There are still no essential features that set man off from the 

 dog, rabbit, or horse, although the various embryos may be 

 distinguished by different proportions of the body parts. 



Beginning with the eighth week of the human embryo, 

 there are important differences of the size and shape of the 

 head that clearly set man apart from the mammals. The cor- 

 respondence which has been noted between man and the 

 mammals continues, now, with the higher apes, the gorilla, 

 and especially the chimpanzee. Not until the seventh or 

 eighth month can the foetuses, as they are now called, of man 

 and the apes be told apart. After passing the plane of the 

 apes, the child enters the heritage of the human races, 

 and it is not until sometime in the ninth month that the 

 racial features are distinguished. Family resemblances 



