362 



R. T. GUNTHER. 



result is not satisfactory. The Pteropods are the butterflies 

 of the sea rather than its dragon-flies ; and the elaborate 

 hydraulics of the Cephalopods effect locomotion by a totally 

 different process, which we are not considering here. 



The separate regions of body merge gently into one 

 another, and all projections unnecessary for functions of 

 swimming or feeding have been smoothed down. For this 



Text-fig. 2. — Grimalditeuthis (from Pelseneer, after Joubin). 

 fi'fji" , lateral and caudal fins. 



reason the visceral sac is all contained within the cigar- 

 shaped contour of the body-wall. In Mollusca the integu- 

 ment of the visceral sac is typically folded near its junction 

 with the head and foot, but no such mantle-flap or pallium is 

 distinguishable in Sagitta. The pallial ectoderm is, however, 

 drawn out in the horizontal plane to form the lateral and 

 caudal fins of many of those Dibranchiate Cephalopoda (text- 

 fig. 2) in which the shell is most degenerate, and the resem- 

 blance is strengthened by the deposition of a chitinous or 



