596 RECORD OF CURRENT RESEARCHES RELATING TO 



of this hypothesis have not, Professor Lankestcr thinks, met with tho 

 consideration which they merit. 



Naturalists have long recognized what is called retrogressive meta- 

 mori^liosis in the case of parasitic animals, and it is the more i-emark- 

 able that the same hypothesis should not have been applied to the 

 explanation of other simple forms of animals. The hypothesi-s of 

 degeneration will, it is believed, render most valuable service in 

 pointing out the true relationships of animals which are a puzzle 

 and a mystery when we use exclusively the hypothesis of Balance 

 or Elaboration. 



Eeferring to tho lizard-like creatures Se/ps and Bipes, which have 

 lost the locomotive organs once possessed by their ancestors, it is 

 pointed out that this very partial or local atrophy is not what the 

 author means by Degeneration ; but if this atrophy is extended to a 

 variety of important organs, we shall then have a thorough-going 

 instance of it. 



Degeneration may be defined as a gradual change of the structure 

 in which the organism becomes adapted to less varied and less complex 

 conditions of life, whilst elaboration is a gradual change of structure 

 in which the organism becomes adapted to more and more varied and 

 complex conditions of existence. In elaboration there is a new 

 expression of form, corresponding to new perfection of work in the 

 animal machine. In degeneration there is suppression of form, cor- 

 responding to the cessation of work. Elaboration of some one organ 

 onay be a necessary accompaniment of degeneration in all the others. 

 In fact, this is very generally the case ; and it is only when the total 

 result of the elaboration of some organs and the degeneration of others 

 is such as to leave the whole animal in a lower condition — that is, 

 fitted to less complex action and reaction in regard to its surround- 

 ings than was the ancestral form with which we are comparing it 

 (either actually or in imagination) — that we speak of that animal as 

 an instance of degeneration. 



Any new set of conditions occurring to an animal which render its 

 food and safety very easily attained, seem to lead as a rule to degenera- 

 tion ; just as an active, healthy man sometimes degenerates when he 

 becomes suddenly possessed of a fortune. The habit of parasitism 

 clearly acts upon animal organization in this way. Let the parasitic 

 life once be secured, and away go legs, jaws, eyes, and ears. The 

 active, highly-gifted crab, insect, or annelid may become a mere sac, 

 absorbing nourishment and laying eggs. 



Some examples of undeniably degenerate animals are examined, 

 amongst which are Sacculina, which infests hermit-crabs, and from its 

 young (nauplius) stage with legs, has become a mere sac filled with 

 eggs, and absorbing nourishment by root-like processes ; Lernceocera, 

 the parasite of the gills of fishes, which has lost the well-developed 

 legs of its early stage and become a worm-like creature ; the 

 cirrhipedes (barnacles), the mites, and the ascidians. 



Special attention is given to the latter, the author's object being 

 to show that their structure and life-history may be best explained on 

 .the hypothesis that they are instances of degeneration, and in fact are 



