i68 



TELEOSTOMES 



well known in the case of Deep-sea Fishes, in their acquir- 

 ing a characteristic shape under the conditions of abyssal 

 life. The head region of these forms becomes greatly- 

 exaggerated in size, and the trunk tapers suddenly away 

 toward the tip of the pointed tail. The tissues become 

 extremely modified, soft, porous, delicate, often trans- 

 parent ; skeletal parts are deficient in lime, and loosely 

 articulated. Many organs are retained in curiously unde- 

 veloped or aborted conditions ; the vertebral axis is noto- 



FigS. 172-174. — Deep-sea fishes. (After GiJNTHER.) 172. Paraliparis bathy- 

 bius. 640 fathoms. 173. Bathyonus compressus. 1400 fathoms. 174. Notacanlhus 

 sexspinis. 1800 fathoms. 



chordal ; gill arches, as many as six (.'' ) in number, may open 

 freely to the surface, never enclosed by opercula ; sensory 

 canals remain as open grooves as in the most generalized 

 fishes ; paired fins are retained either in an undeveloped 

 condition or are not produced at all. Absence of light has 

 been not without its effects ; body colours are usually dark 

 and meaningless ; while, on the other hand, when eyes still 



