PRESIDENTIAL ADDRESS. 31 



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 

 condition. Food yolk, the great cause of distortion in development, is 

 almost absent, and there is not the slighest 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. 



Our knowledge of the conditions leading to degeneration is un- 

 doubtedly incomplete, but it must be 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 com- 

 pared with other vertebrates is one of the very few points that can be 

 referred to as possibly indicating degeneration, and will be considered 

 more fully at a later point in my address. 



A consideration of much less importance, but deserving of mention, 

 is that in its mode of life Amphioxus not merely differs as already 

 noticed from those groups of animals which we know to be degenerate, 

 but agrees with some, at any rate, of those which there is reason to 

 regard as primitive or persistent types. Amphioxus, like Balanoglossus, 

 Lingula, Dentalium, and Liraulus, is marine, and occurs in shallow 

 water, visually with a sandy bottom, and, like the three smaller of these 

 genera, it lives habitually buried almost completely in the sand, into 

 which it burrows with great rapidity. 



I do not wish to speak dogmatically. I merely wish to protest 

 against a too ready assumption of degeneration ; and to repeat that, so 

 far as I can see, Amphioxus has not yet, either in its development, in 

 its structure, or in its habits, been shown to present characters that 

 suggest, still less that prove, the occurrence in it of general or ex- 

 tensive degeneration. 



