3i6 THE RECAPITULATION THEORY 



extraordinary nature of the segmentation of the 

 egg of Peripatus capensis, made known to us 

 through Mr. Sedgwick's admirable researches, may 

 be due to loss of food yolk : a suggestion which 

 receives support from the long duration of uterine 

 development in this case. Our knowledge is very 

 imperfect as to the ease with which food yolk may 

 be acquired or lost ; but until our information is 

 more precise on this point it seems unwise to lay 

 much stress on suggested pedigrees which involve 

 great and frequent alternations in the amount of 

 food yolk present. 



f _ Ofjrauses other than food yolk, or only in- 

 directly connected with it, which tend to falsify the 

 ancestral history, many are now known, but time 

 will only permit me to notice the more important. 

 These are distortion, whether in time or space ; 

 sudden or violent metamorphosis ; a series of 

 "modifications, due chiefly to mechanical causes, and 

 which may be spoken of as developmental con- 

 Veniences ; the important question of variability 

 in development ; and finally the great problem of 

 degeneration. 



Concerning distortions in time, all embryologists 

 have noticed the tendency to anticipation or pre- 

 cocious development of characters which really 

 belong~to a later stage in the pedigree. The 

 early attainment of the cyclical form in the shell 

 of Orbitolites complanata is a case in point ; and 

 Wiirtenberger has specially noticed this tendency 

 in Ammonites. Many early larvae show it mark- 

 edly, the explanation in this case being that it is 



