248 Notes, iv. 13. 



exceptional position of its gall-bladder ; but probably he had not examined it often, 

 for he speaks of it as being rare (//. A. vi. 17, 9). 



6. Cf. iv. 12, Note 11. At first one is struck with admiration at the prescience of A. 

 in identifying the pectoral and ventral fins with the anterior and posterior limbs of other 

 Vertebrata ; and one is inclined to credit him with a much more accurate conception of 

 homologies than he really possessed. Not a single word, however, is said of any 

 anatomical correspondence of fin and limb. The identification is based on similarity of 

 function, not on similarity of formation ; that is to say, it is founded on analogies, and. 

 not on homologies. It is true that the other fins, which are not homologous to limbs, 

 are passed over by A. notwithstanding their analogous office ; but this is only owing 

 to the fact that they are single, that is unpaired. How little comparative anatomy had 

 to do with A.'s statement is shown by his overlooking the real pectorals in the rays, and 

 imagining their dorsals, which are merely cutaneous appendages, to be the pectorals 

 misplaced. So also he speaks of the serpents, which have no limbs at all, as still 

 reseml;ling the other sanguineous animals, i.e. in having four points of motion. " For," 

 says he, "their flexures are four," while in such fishes as have only two fins "the 

 flexures are two, to replace the missing pair" (cf. H. A. i. 5, 15). 



7. It is strange and yet, as it appears to me, indisputably true, that A. was perfectly 

 ignorant of the fact that tadpoles are the larval forms of frogs and newts. For it is 

 impossible that he can have known it, and yet made no mention of what would have 

 seemed to him, as indeed it is, a most extraordinary phenomenon. He appears to have 

 looked on tadpoles as aberrant kinds of fishes, and on frogs of course as reptiles. 



8. Destitute, that is, of fin-rays, such as exist in the caudal fin of fishes. Elsewhere 

 {H. A. i, 5, 10) A. compares the tadpole's tail to that of Silurus glanis, referring, as I 

 suppose, to the fact that in Silurus the anal fin is of great length, extending along the 

 whole belly, and joins, or nearly joins, with the caudal fin, so as to resemble the ventral 

 part of the continuous fin of the tadpole. 



9. The Batos is described as a flat cartilaginous fish, with rough skin, and long rough 

 tail {H. A. vi. 10, 17) ; as hiding itself under the sand and then, by means of certain 

 oral processes, attracting small fishes on which it preys (^H. A. ix. 37, 5). Lastly, it is 

 said to copulate with a different species of fish, called Rhine, and thus to give origin to a 

 mongrel, the Rhinobatus {H. A. vi. 11, 7). 



The Rhine is said to be a cartilaginous fish, whether flat or elongated is not expressly 

 stated, with a thick tail ; producing young twice a year {^H. A. v. 10, i), and resembling 

 the Batos in hiding under sand and in its method of attracting prey by means of its 

 oral processes {/T. A. ix. 37, 5). It has moreover the power of changing its colour, in 

 adaptation to the stones, etc., about it ; and is the only fish that can do this {^H. A. 

 ix. 37, 22). 



These data are insufilcient for exact determination of the species meant. It is usual, 

 however, to identify Rhine with the angel-fish, and Batos with some or other ray. 

 Numerous rays, as also the angel-fish, hide themselves as described under sand or stones. 

 The angel-fish has also some small processes in front, which might be those which A. 

 supposes to be used to allure small fishes {YarrelPs Fishes, ii. 407). But I know of 

 nothing similar in a ray, to suit the statement as to Batos. As regards the power of 

 changing colour, the angel-fish, says Yarrell, "is probably liable to some variation in 

 colour depending on the nature of the ground in the locality in which it is found." This 

 tallies well with A.'s account of Rhine. But it must be remembered that a similar 

 faculty of adapting the colour of the skin to that of the ground belongs to many other 

 fishes. I have frequently, for instance, watched its operation in the plaice j which fish 

 changes its hue very completely and very quickly. 



