336 THE RECAPITULATION THEORY 



closely, because in their case the suggestion of 

 degeneration is admittedly put forward as a means 

 of escape from difficulties arising through theoretical 

 views concerning the relation between vertebrates 

 and invertebrates. Amphioxus itself, so far as I 

 can see, shows in its development no sign of 

 degeneration, except possibly with regard to the 

 anterior gut diverticula, whose ultimate fate is not 

 altogether clear. With regard to the earlier stages 

 of development, concerning which, thanks to the 

 patient investigations of Kowalevsky and Hatschek, 

 our knowledge is precise, there is no animal known 

 to us in which the sequence of events is simpler or 

 more straightforward. Its various organs and 

 systems are formed in what is recognised as a 

 primitive manner ; and the development of each is 

 a steady upward progress towards the adult con- 

 dition. Food yolk, the great cause of distortion in 

 development, is almost absent, and there is not the 

 slightest indication of the former possession of a 

 larger quantity. Concerning the later stages our 

 knowledge is incomplete, but so much as has been 

 ascertained gives no support to the suggestion of 

 general degeneration. 



t Our knowledge of the conditions leading to 

 degeneration is undoubtedly incomplete, but it must 

 J>e noticed that the conditions usually associated 

 with degeneration do not occur. Amphioxus is not 

 parasitic, is not attached when adult, and shows no 

 evidence of having formerly possessed food yolk 

 in quantity sufficient to have led to the omission 

 of important ancestral stages. Its small size, as 



