100 



CHAPTERS ON EVOLUTION. 



lately tailless as man. One has but to compare the young crab with 

 the adult, or the fish-like tadpole with the frog (Fig. 48), to witness a 

 most typical case of the disappearance of a tail. And it is worth 

 remembering that the frogs have the advantage of humanity in point 

 of antiquity; since the advancement of the tailed tadpole race to 

 become the tailless frogs of to-day must have taken place, according 

 to geological evidence, long ages anterior to the advent of the 

 " imperial race " of man. 



But if so much may be proved and said regarding the rudi- 

 mentary nature of " tails," it must also be borne in mind that the 

 opposite case of a special development of the tail in man is by no 

 means unknown. Occasionally in the human subject a short but 

 free tail is found to be developed, this fact constituting at once a 

 surgical abnormality and a physiological "reversion" to an ancient 

 order of things. Let us consider for a moment what development 

 teaches us concerning the exact place assumed by the end of the spine 

 in higher animals. Primarily, we are struck by the close resemblance 

 to each other presented by the embryos or young of vertebrate 

 animals (Fig. 37) in. their earlier stages of development. Even Von 



Baer himself, an 

 authority in mat- 

 ters relating to 

 embryology, said 

 of this likeness 

 that " the em- 

 bryos of mam- 

 malia, of birds, 

 lizards, and 

 snakes, and pro- 

 bably also of 



Chelonia (tortoises and turtles), are, in their earliest states, exceedingly 

 like one another, both as a whole and in the mode of development of 

 these parts ; so much so, in fact, that we can often distinguish the 

 embryos only by their size. In my possession," he continues, " are 

 two little embryos in spirit, whose names I have omitted to attach, 

 and at present I am quite unable to say to what class they belong. 

 They may be lizards, or small birds, or very young Mammalia, so 

 complete is the similarity in the mode of formation of the head and 

 trunk in these animals. The extremities, however, are still absent in 

 these embryos. But even if they had existed in the earliest stage of 

 their development, we should learn nothing, for the feet of lizards 

 and mammals, the wings and feet of birds, no less than the hands 

 and feet of man, all arise from the same fundamental form." The 

 close likeness between vertebrates in their early stages of growth, so 

 plainly lescribed in Von Baer's words, extends to the caudal or tail- 



PlG. 



CALF. [Fie. 37.] RABBIT. 



