PRESIDENTIAL ADDRESS. 20 



So is it also with animals : the survival of a form that is ideally 

 inferior is very possible. To animals living in profound darkness the 

 possession of eyes is of no advantage, and forms devoid of eyes would 

 not merely lose nothing thereby, but would actually gain, inasmuch as 

 they would escape the dangers that might arise from injury to a 

 delicate and complicated organ. In extreme cases, as in animals 

 leading a parasitic existence, the conditions of life may be such as to 

 render locomotor, digestive, sensory, and other organs entirely useless ; 

 and in such cases those forms will be best in harmony with their 

 surroundings which avoid the waste of energy resulting from the 

 formation and maintenance of these organs. 



Animals which have in this way fallen from the high estate of their 

 forefathers, which have lost organs or systems which their progenitors 

 possessed are commonly called degenerate. The principle of degenera- 

 tion, recognised by Darwin as a possible, and, under certain conditions, 

 a necessary consequence of his theory of natural selection, has been 

 since advocated strongly by Dohrn, and later by Lankester in an 

 Evening Discourse delivered before the Association at the Sheffield 

 Meeting in 1879. Both Dohrn and Lankester suggested that de- 

 generation occurred much more widely than was generally recognised. 



In animals which are parasitic when adult, but free swimming in 

 their early stages, as in the case of the Rhizocephala, whose life history 

 was so admirably worked out by Fritz Miiller, degeneration is clear 

 enough : so also is it in the case of the solitary Ascidians, in which the 

 larva is a free swimming animal with a notochord, an elongated tubular 

 nervous system, and sense organs, while the adult is fixed, devoid of 

 the swimming tail, with no notochord, and with a greatly reduced 

 nervous system and aborted sense organs. 



In such cases the animal, when adult, is, as regards the totality of 

 its organisation, at a distinctly lower morphological level, is less highly 

 differentiated than it is when young, and during individual develop- 

 ment there is actual retrograde development of important systems and 

 organs. 



About such cases there is no doubt ; but we are asked to extend the 

 idea of degeneration much more widely. It is urged that we ought not 

 to demand direct embryological evidence before accepting a group as 

 degenerate. We are reminded of the tendency to abbreviation or to 



