II.] INCIPIENT STRUCTURES. 43 



absence of their remains from the secondary strata; never- 

 theless that absence is noteworthy, seeing that existing fish 

 families, e.g. sharks (Squalidse), have been found abundantly 

 even down so far as the carboniferous rocks, and traces of 

 them in the Upper Silurian. 



Another difficulty seems to be the first formation of the 

 limbs of the higher animals. The lowest Vertebrata 1 are 

 perfectly limbless ; and if, as most Darwinians would pro- 

 bably assume, the primeval vertebrate creature was also 

 apodal, how are the preservation and development of the 

 first rudiments of limbs to be accounted for such rudi- 

 ments being, on the hypothesis in question, minute and 

 functionless ? 



In reply to this it has been suggested that a mere flatten- 

 ing of the end of the body has been useful, such, e.g. y as we 

 see in sea-snakes, 2 and that this flattening might have thus 

 constituted the rudiment of a tail formed strictly to aid in 

 swimming. Also that a mere roughness of the skin might 

 be useful to a swimming animal by holding the water 

 better, that thus minute processes might be selected and 

 preserved, and that, in the same way, these might be 

 gradually increased into limbs. But it is, to say the least, 

 very questionable whether a roughness of the skin, or 

 minute processes, would be useful to a swimming animal ; 

 the motion of which they would as much impede as aid, 

 unless they were at once capable of a suitable and appro- 



1 The term " Vertebrata" denotes that large group of animals which are 

 characterized by the possession of a spinal column, commonly known as 

 the "backbone." Such animals are ourselves, together with all beasts, 

 birds, reptiles, frogs, toads, and efts, and also fishes. 



2 It is hardly necessary to observe that these " sea-snakes " have no 

 relation to the often-talked-of "sea-serpent." They are small, venomous 

 reptiles, which abound in the Indian seas. 



