PHYLOGENY. 105 



more downward step is seen in the next succeeding 

 order of the Lophobranchii. The branchial hyoid ap- 

 paratus is reduced to a few cartilaginous pieces, and the 

 branchial fringes are much reduced in size. In the 

 Hippocampidae the caudal fin disappears and the tail 

 becomes a prehensile organ by the aid of which the 

 species lead a sedentary life. The mouth is much con- 

 tracted and becomes the anterior orifice of a suctorial 

 tube. This is a second line of unmistakable degen- 

 eracy among true fishes. 



The Acanthopterygia with pectoral ventral fins pre- 

 sent us with perhaps ten important ordinal or subordi- 

 nal divisions. Until the paleontology of this series is 

 better known, we shall have difficulty in constructing 

 phylogenies. Some of the lines may, however, be 

 made out. The accompanying diagram will assist in 

 understanding them. 



The Anacanthini present a general weakening of 

 the organization in the less firmness of the osseous 

 tissue and the frequent reduction in the size and char- 

 acter of the fins. The caudal vertebrae are of the 

 diphycercal type. As this group does not appear early 

 in geological time, and as it is largely represented now 

 in the abyssal ocean fauna, there is every reason to 

 regard it as a degenerate type.^ The Heterosomata 

 (flounders) found it convenient to lie on one side, a 

 habit which would appear to result from a want of mo- 

 tive energy. The fins are very inefficient organs of 

 movement in them, and they are certainly no rivals for 

 swift-swimming fishes in the struggle for existence, 

 excepting as they conceal themselves. In order to see 

 the better while unseen, the inferior eye has turned in- 



1 The general characters of the deep-sea fish-fauna are those of degen- 

 eracy. 



