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. Paralipans bathy- 

 bius. 640 fathoms. 173. Bathyonus compressus. 1400 fathoms. 174. Notacant/ius 

 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 



