234 



Crcas'urw of Natural 



have been the effect if both arm and fore- 

 arm had also extended freely from the side 

 ! of the fish, and dangled as a long flexible 

 ] many -jointed appendage in the water ? This 

 ; higher development, as it is termed, in rela- 

 ; tion to the prehensile limb of the denizen of 

 ; dry land, would have been an imperfection 

 i in the structure of the creature which is to 

 cleave the liquid element : in it, therefore, 

 : the fore limb is reduced to_ the smallest pro- 

 ! portions consistent with its required func- 

 ! tions : the brachial and antibrachial seg- 

 1 ments are abrogated, or hidden in the trunk : 

 the hand alone projects, and can be applied, 

 1 when the fish darts forwards, prone and flat, 

 by flexion of the wrist, to the side of the 

 trunk ; or it may be extended at right 

 angles, with its flat surfaces turned forwards 

 i and backwards, so as to check and arrest 

 more or less suddenly, according to its clc- 

 , gree of extension, the progress of the fish ; 

 i its breadth may also be diminished or in- 

 ' creased by approximating or divaricating 

 the rays.. In the act of flexion, the fin 

 ! slightly rotates and gives an oblique stroke 

 ! to the water. For these functions, however, 

 the hand requires as much extra develop- 

 ment in breadth, as reduction in length and 

 thickness ; and mark how this is given to 

 the so-called embryo or rudimcntal fore- 

 limb s it is gained by the addition of ten, 

 twenty, or it may be even a hundred digital 

 rays, beyond the number to which the fingers 

 are restricted, in the hand of the liigher 

 i classes of Vertebrata. We find, moreover, 

 ! RS numerous and striking modifications of 

 the pectoral fins, in adjustment to the pe- 

 i culiar habits of the species in Fishes, as we 

 i do in the fore limbs in any of the higher 

 ! classes. This fin may wield a formidable 

 and special weapon of olfence, as in many 

 Siluroid fishes. But the modified hands 

 have a more constant secondary office, that 

 of touch, and arc applied to ascertain the 

 nature of surrounding objects, and particu- 

 larly the character of the bottom of the 

 water in which the fish may live. You may 

 witness the tactile action of the pectoral fins 

 when gold fish are transferred to a strange 

 vessel : their eyes are so placed as to prevent 

 their seeing what is below them ; so they 

 compress their air-bladder, and allow them- 

 selves to sink near the bottom, which they 

 sweep, as it were, by rapid and delicate vi- 

 brations of the pectoral fins, apparently 

 ascertaining that no sharp stone or stick 

 projects upwards, which might injure them 

 in their rapid movements round their pri- 

 son." * * * " Everywhere, whatever re- 

 ! semblance or analogy we may perceive in 

 the ichthyic modification* of the Vertebrate 

 skeleton to the lower forms or the embryos 

 of the higher classes, we shall find such ana- 

 logies to be the result of special adaptations 

 for the purpose or function for wliich that 

 part of the fish is designed. 



" The ventral fins or homologues of the 

 hind legs are still more rudimental still 

 more embryonic, having in view the com- 

 parison with the stages of development in a 

 land animal than the pectoral fins ; and 

 their small proportional size reminds the 

 homologist of the later appearance of the 



hind limbs, in the development of the land 

 Vertebrate. But the hind limbs more im- 

 mediately relate to the support and pro- 

 gression of an animal on dry land than the 

 fore limbs : the le<s are the sole terrestrial 

 locomotive organs in Birds, whose fore-limbs 

 are exclusively modified, as wings, for mo- 

 tion in another element. The legs are the 

 sole organ of support and progression in 

 Man, whose pectoral members or arms are 

 liberated from that office, and made entirely 

 &ubservient to the varied purposes to which 

 an inventive faculty and an intelligent will 

 would apply them. To what purpose, then, 

 encumber a creature, always floating in a 

 medium of nearly the same specific gravity 

 as itself, with hind limbs ? They could be 

 of no use ; nay, to creatures that can only 

 attain their prey, or escape their enemy, by 

 vigorous alternate strokes of the hind part 

 of the trunk, the attachment there of long 

 flexible limbs would be a grievous hindrance, 

 a very monstrosity. So, therefore, we find 

 the All-wise Creator has restricted the de- 

 velopment and connections of the hind limbs 

 of Fishes to the dimensions and to the form 

 which, whilst suited to the limited functions 

 they are capable of in this class, would pre- 

 vent their interfering with the action of 

 more important parts of the locomotive ma- 

 chinery." 



" The following short account of some 

 experiments upon fish, made for the purpose 

 of ascertaining the use of their fins, I give 

 (says Mr. Owen) in the words of their gifted 

 describer, PALEY, to whom Comparative 

 Physiology owes many beautiful accessions 

 to its ideological applications. ' In most fish, 

 beside the great fin the tail, we find two 

 pairs of fins upon the sides, two single fins 

 upon the back, and one upon the belly, 

 or rather between the belly and the tail. 

 The balancing use of these organs is proved 

 in this manner. Of the large-headed fish, if 

 you cut off the pectoral fins, that is, the pair 

 which lies close behind the gills, the head 

 falls prone to the bottom ; if the right pec- 

 toral fin only be cut off, the fish leans to 

 ; if the 



that side ; 



entral fin on the same side 



be cut away, then it loses its equilibrium 

 entirely ; if the dorsal and anal fins be cut 

 off, the fish reels to the right and left : when 

 the fish dies, that is, when the fins cease to 

 play, the belly turns upwards. The use of 

 the same parts for motion is seen in the fol- 

 lowing observation upon them when put 

 into action. The pectoral, and more parti- 

 cularly the ventral fins, serve to raise and 

 depress the fish; when the fish desires to 

 have a retrograde motion, a stroke forward 

 with the pectoral fin effectually produces 

 it ; if the fish desire to turn either way, a 

 single blow with the tail the opposite v;ay 

 sends it round at once ; if the tail strike 

 both ways, the motion produced by the dou- 

 ble lash is progressive, and enables the fish 

 to dart forwards with an astonishing velo- 

 city. The result is not only in some cases 

 the most rapid, but in all cases the most 

 gentle, pliant, easy animal motion with 

 which we are acquainted. However, when 

 the tail is cut off, the fish loses all motion, 

 and it gives itself up to where the water 



