180 FISHES. 



iug a white colour when preserved in spirits, resembling a 

 tapeworm, being quite as soft and flexible. The skeleton is 

 entirely cartilaginous, or slight ossifications are only now and 

 then visible, especially towards the end of the vertebral 

 column. The latter is replaced by a chorda dorsalis which, 

 in many specimens, is found to be divided into numerous 

 segments. Neural arches are sometimes present in their 

 rudimentary condition. The anterior end of the chorda 

 passes into the cartilaginous base of the skull, the connec- 

 tion not being by means of joint and ligaments. Haemal 

 arches are found on the caudal portion. Eibs none. The 

 skull, like the vertebral column, is nearly entirely cartila- 

 ginous. The basi-sphenoid, frontal, and jaw-bones are the 

 first which may be distinguished, and the mandible has 

 generally ossifications. 



The muscles are generally not attached to the chorda, 

 which is surrounded by a thick gelatinous mass, separating 

 the lateral sets of muscles from each other. These muscles 

 are attached to the external integument, each forming; a thin 

 flat angular band, the angle being directed forwards. How- 

 ever, specimens are frequently found in Avhich the muscles 

 are more developed, evidently at the expense of the gela- 

 tinous matter, which is diminished in quantity. They are 

 attached to the chorda, and the entire fish has a more cylin- 

 drical form of the body {Hdmiclithys). 



The nervous, circulatory, and respiratory organs are well 

 developed. In those with a sub-cylindrical body the blood 

 is red, in those with a flat body the blood-corpuscles show 

 but rarely a faint coloration. There are four branchial 

 arches, and in some {Tilurus) psevidobrauchiaj have been 

 found. The gill-openiugs are more or less narrow. The 

 nostrils are double on eacli side, and the posterior is close 

 to the eye. 



The stomach has a large blind sac, and in Leptocephalus 



