I5t> REPRESENTATION OF PROTOMORPHIC ALTERNATION 



VI 



REPRESENTATION OF PROTOMORPHIC ALTER- 

 NATION IN THE EMBRYOGENY OF THE 

 HIGHER ANIMALS. 



1 . IN the foregoing remarks traces of reproduction by the 

 co-operation of the sexes have been noticed, in all the leading 

 groups of both kingdoms, of nature. This process still con- 

 tinues to exist, side by side with that of gemmation, even in 

 those lower forms of life, in which the latter is much the 

 most conspicuous mode of propagation. Hence the enquiry 

 naturally suggests itself, whether in the higher species, in 

 which sexual generation is the only well-marked agency for 

 the purpose of propagation, any associated phenomena 

 occur which can be considered as corresponding to the gem- 

 mation of the inferior classes ; and whether the alternation 

 of the two processes, so striking in some of the lower forms, 

 has any representation in the case of the higher organisms, 

 and of those generally in which naturalists have recorded 

 no change in the forms propagated from each other. In 

 reply, it may be observed that on a careful survey of the 

 phenomena of reproduction in the principal groups of or- 

 ganized beings, indications do present themselves of a ge- 

 neral tendency in this direction, as will appear from some 

 illustrations which will now be offered, and which go to 

 show that in the phenomena of embryological development, 

 and of the maturation of the sexual organs, processes occur 

 which have a certain correspondence with those observed in 

 the best marked cases of alternation of generations. 



