490 THE INDIVIDUAL AND THE RACE: 



in individual development and steps in racial evolution. A 

 tadpole is from the first in several ways an Amphibian and 

 not a Fish, and yet in its two-chambered heart and branchial 

 circulation it is for a time distinctively piscine. 



One reason why the ontogenetic recapitulation of phylogeny 

 must be general, not precise, is that the successive gains made 

 in the course of racial evolution are not superposed one upon 

 another, but must be severally incorporated into the organi- 

 sation and unified with it. The additions from millennium 

 to millennium are not like new wings added to a house, 

 for the tenements which we call individuals are continually 

 dissolved, and there is re-unification at the start of each new 

 life. We must remember too that antique characters grad- 

 ually disappear, thus ancestral birds had teeth, but no embryo 

 bird shows any trace of them. These saving-clauses are 

 of importance, but the broad fact remains that the organism's 

 inheritance, garnered for ages, does in many cases express 

 itself in a step-to-step development, from the general to the 

 special, which is in some measure a recapitulation of stages 

 in what is believed to have been the racial evolution. Some 

 illustrations must be given. 



On each side of the neck of the embryo reptile, bird, and 

 mammal there are branchial pouches or gill-clefts which 

 correspond to those which have a respiratory function in am- 

 phibians and fishes, and may or do persist throughout life. 

 In reptiles, birds, and mammals these pouches are on the 

 whole transient, like fleeting reminiscences. The first seems 

 to persist as the Eustachian tube from the auditory passage 

 to the back of the mouth, and the thymus gland is connected 

 with another ; but the rest pass away without persistent re- 

 sult. They are echoes of the past. In embryos of the chick 

 and of some reptiles, dwindling and transient traces of gills 



