MOLLUSCA : CEPHALOPODA. 347 



is forcibly expelled through the funnel, which is provided 

 with a valve permitting the egress of water, but preventing its 

 ingress. By a repetition of this process, not only is respiration 

 effected but locomotion is simultaneously subserved ; the jets 

 of water expelled from the funnel, by their reaction, driving 

 the animal in the opposite direction. 



The nervous system is formed upon essentially the same 

 plan as in the other Mollusca, but it is more concentrated, and 

 the supra-cesophageal or cerebral ganglia are protected by a 

 cartilage, which is to be regarded as a rudimentary cranium. 

 This structure, therefore, presents us with the nearest approach 

 which we have yet met with to the Vertebrate type of organi- 

 sation. At the base of the cartilaginous cranium are two 

 chambers, each containing a membranous sac with an otolith ; 

 and the auditory nerves pass from the cerebral ganglia into the 

 auditory chambers to reach the auditory sacs. The eyes are 

 highly organised, and exhibit a sclerotic, choroid, retina, vitreous 

 humour, aqueous humour, and lens. 



The sexes in all the Cephalopoda are in different individuals, 

 and the reproductive process in the Dibranchiate section of 

 the class (Cuttle-fishes) is attended with some very singular 

 phenomena. In this order the ducts of the generative organs 

 open into the pallial chamber, and each individual, besides 

 the essential organs of reproduction (testis or ovary), gene- 

 rally possesses an accessory gland ; that of the female secret- 

 ing a viscid material which unites the eggs together, whilst 

 that of the male coats the spermatozoa, and aggregates them 

 into peculiar worm-like filaments, termed " spermatophores," 

 or the " moving filaments of Needham." The spermatophore 

 is filled with spermatozoa, and possesses the power of ex- 

 panding when moistened, rupturing, and expelling the con- 

 tained spermatozoa with considerable force. During the 

 congress of the sexes the male transfers the spermatophores to 

 the pallial chamber of the female, true intromission not being 

 possible. Further, in all the male Cuttle-fishes one of the 

 arms is specially modified to subserve reproduction ; being 

 in many cases so altered as to become useless as a locomotive 

 organ. The arm so affected, in the more striking forms, is 

 said to be " hectocotylised," and like the metamorphosed 

 palpi of the male spiders it selves to convey the seminal 

 fluid to the female. The mode in which this is effected varies 

 in different species. Thus, in the male Octopus (the Poulpe) 

 the third right arm is primitively developed in a cyst, which 

 ultimately ruptures and liberates the metamorphosed arm, 

 which then appears to be of greater size than the correspond- 



