Species in the case of certain Fishes. 445 



tions introduced by circumstances into the organs of jjrehcn- 

 sion, and endeavour to trace as far as possible some of the 

 correlative compensations necessarily superinduced in other 

 ])arts of the organism. We may even reduce our field of 

 observation to the investigation of these organs in certain 

 fishes, as indicated in the title of this note. 



2o attain the same end^ nature must sometimes employ^ ac- 

 cording to circumstances^ very different means ; moreover^ even 

 with identical means, it often happens that, under different 

 circumstances, the correlative modifications are not effected 

 alike, sometimes in different individuals of the same species, 

 sometimes in the different parts of the same individual. 



The organs of prehension, so varied in the animal kingdom, 

 being, in the fishes, represented by the mouth alone, one can 

 easily understand the influence that may be gradually exerted 

 upon the arrangement and proportions of this buccal cleft in 

 the first place, and then upon the whole organization of the 

 individual, by the modifications introduced into the actions 

 and " gymnastic " of the animal by the necessarily different 

 mode of prehension to which it must adapt itself in order to 

 procure its nourishment in one condition or position or another 

 — above or below it, at the surface or the bottom of the water, 

 for example. 



A mere glance at a few marine fishes will amply suffice to 

 show us many different aspects of the buccal pieces appro- 

 priated to one mode of prehension or another ; we have only 

 to consider, for example, the comparative forms of the body, 

 or of the limbs and jaws, in the genera Xiphias, Histiophorus, 

 Centriscus, and Belone. But under conditions more like those 

 of our own country, the freshwater species may also show us 

 various forms of the mouth adapted to different uses. As I 

 shall have to revert to these, I shall confine myself here to 

 referring en passant to the case of Toxotes jaculator, which 

 takes its prey at the surface, and often even provokes the fall 

 of the insects on which it feeds by projecting a drop of water 

 at those which are placed above the liquid. For this purpose 

 this fish has the lower jaw considerably prominent and turned 

 up, and at the same time the fins placed far enough back to 

 allow the entire head of the animal to be easily kept raised 

 into the air. If I cared to go beyond the class which parti- 

 cularly occupies our attention I might also recall the fact that 

 those birds which are condemned, without swimming, to seek 

 their nourishment at the bottom of the water, have the legs, 

 the neck, and the beak all greatly elongated ; whilst in those 

 which, like the snipe, for example, are called upon to rum- 

 mage beneath them, not at the bottom of the water, but only in 



