aso 



ZOOLOGY. 



f>-?. 





appeared. The squids or cuttle-fisli are very active, some- 

 times leaping out of the water and falling on the decks of 

 large vessels. They dart rapidly back- 

 ward by ejecting the water from their 

 siphon or funnel. 



The Cephalopods are divided into 

 two orders, according to the number of 

 their gills. 



Order 1. Tetrairancldata. — This 

 group, in which the gills are four in 

 number, is represented by the Nautilus, 

 the sole living representative of a num- 

 ber of fossil forms, such as Ortlioceras^ 

 Goniatites and Ammonites. 



Nautilus pom/pilius Linn. (Pig. 222), 

 and Nautilus umbilicatuhis are the 

 only survivors of about 1500 extinct 

 species of the order. 



Order 2. Dihrancliiata. — The Di- 

 Irancldates are so called from possessing but two gills, while 

 the Tetrahranchiates had, as in Nautilus, numerous unarmed 

 tentacles ; these are now represented by ten (Decapoda). or 



Fig. 219. — Same as Fig, 

 218, but farther advanced. 



Fig. 220. 



Fig. 221. 



Fig. 220.— Development of an unknown euttle-flsh. v, velum ; y, yolk ; mt, man- 

 Lie beginning to develop. 



Fig. 221.— The same, much farther advanced, a, a\ a", arms ; ?«, mouth ; br. bi\ 

 gills ; /, funnel ; /(, ear ; ^, optic ganglion ; mt, mantle, the dotted line ending in a 

 chromatophore.— After Grenachcr. 



eight {Octopoda) aims, provided with numerous suckers. To 

 the ten-armed forms belong tSpirula, a diminutive cuttle, with 



