CHAPTER VI 



THE CEPHALOPODA 



CLASS V. THE CEPHALOPODA, CUVIER. 



Order 1. Tetrabranchia. 

 Sub-Order 1. Nautiloidea. 

 ,, 2. Ammonitoidea. 



Order 2. Dibranchia. 

 Sub-Order 1. Decapoda. 

 Tribe 1. Oigopsida. 

 2. Myopsida. 

 Sub-Order 2. Octopoda. 

 Tribe 1. Leioglossa. 

 ,, 2. Trachyglossa. 



Definition. The Cephalopoda are perfectly symmetrical Mollusca, 

 in which the edges of the foot are transformed into circumoral 

 appendages completely surrounding the head, and the epipodium 

 is modified to form an exhalant muscular tube or funnel consisting 

 of two free or united lobes, situated behind the head at the opening 

 of the pallial cavity, and serving as a conduit for the water from 

 this cavity. In the nervous system all the typical ganglion-pairs 

 are concentrated in the head, and are applied to or contained in 

 the interior of a cartilaginous skeletal piece. The renal organs are 

 constituted by the glandular covering of the afferent branchial 

 vessels. ^The coelom communicates with the exterior either directly 

 or by the intermediary of the paired kidneys, and by a second pair 

 of ducts serving as gonaducts. The gonad is situated in the coelom 

 and is not continuous with the gonaducts. A portion of the 

 circumoral pedal crown is " hectocotylised," that is to say, modified 

 to form a copulatory organ in the male. The development is 

 characterised by the incomplete segmentation of the ovum. 



I. GENERAL DESCRIPTION AND EXTERNAL CHARACTERS. 



In comparing the Cephalopoda with other Mollusca, one finds 

 that the ventral surface is much abbreviated and the length of the 



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