MUTUAL AFFINITIES OF ORGANIC BEINGS 405 



age than that at which they first appeared. It should also be borne 

 in mind, that the law may be true, but yet, owing to the geological 

 record not extending far enough back in time, may remain for a 

 long period, or forever, incapable of demonstration. The law will 

 not strictly hold good in those cases in which an ancient form be- 

 came adapted in its larvae state to some special line of life, and 

 transmitted the same larval state to a whole group of descendants ; 

 for such larval will not resemble any still more ancient form in its 

 adult state. 



Thus, as it seems to me, the leading facts in embryology, which 

 are second to none in importance, are explained on the principle 

 of variations in the many descendants from some one ancient pro- 

 genitor, having appeared at a not very early period of life, and 

 having been inherited at a corresponding period. Embryology 

 rises greatly in interest, when we look at the embryo as a picture, 

 more or less obscured, of the progenitor, either in its adult or larval 

 state, of all the members of the same great class. 



RUDIMENTARY, ATROPHIED AND ABORTED ORGANS 



Organs or parts in this strange condition, bearing the plain 

 stamp of inutility, are extremely common, or even general, 

 throughout nature. It would be impossible to name one of the 

 higher animals in which some part or other is not in a rudimen- 

 tary condition. In the mammalia, for instance, the males possess 

 rudimentary mammae ; in snakes one lobe of the lungs is rudimen- 

 tary; in birds the "bastard-wing" may safely be considered as a 

 mdimentary digit, and in some species the whole wing is so far 

 rudimentary that it cannot be used for flight. What can be more 

 curious than the presence of teeth in foetal whales, which when 

 grown up have not a tooth in their heads; or the teeth, which 

 never cut through the gums, in the upper jaws of unborn calves? 



Rudimentary organs plainly declare their origin and meaning 

 in various ways. There are beetles belonging to closely allied 

 species, or even to the same identical species, which have either 

 full-sized and perfect wings, or mere rudiments of membrane, 

 which not rarely lie under wing-covers firmly soldered together; 

 and in these cases it is impossible to doubt that the rudiments 

 represent wings. Rudimentary organs sometimes retain their po- 

 tentiality: this occasionally occurs with the mammae of male 

 mammals, which have been known to become well developed and 

 to secrete milk. So again in the udders in the genus Bos, there 

 are normally four developed and two rudimentary teats; but the 

 latter in our domestic cows sometimes become well developed 



