CEPHALOPODA 



6oi 



pro- 



In LoUgo there is only a horny pen^ which represents the 

 ostracam, while in the Octopoda there is no skeleton at all. 



The Dibranchiata are specialized in two ways. The first is for a 

 pelagic life; their bodies become elongated, fins develop and they 

 become transparent. They may, exceptionally, develop such speed in 



Fig. 411. External appearance of Dibranchiata. a. Octopus swimming back- 

 ward, b, Octopus asleep, c, Sepia swimming gently, d, Loligo in the act of 

 catching prey, e, Sepia becoming active. 



the water that they take off from the surface and glide for considerable 

 distances through the air, in the mariner of the flying fish, aided by 

 their spreading fins (Todarodes Sagittarius). Loligo (Fig. 411 ^) is a 

 well-known example of the pelagic type and may be seen in aquaria 

 swimming in troops, keeping their distances and turning with military 

 precision. 



