272 MANUAL OF ZOOLOGY. 



like gills, placed on the sides of the body in a branchial cavity 

 which opens anteriorly on. the under surface of the body. At 

 the base of each gill, in the Cuttle-fishes, is a special contrac- 

 tile cavity, whereby the venous blood, returned from the 

 body, is driven through the branchiae. In addition to these 

 accessory organs the so-called ' branchial hearts ' there is 

 a true systemic heart, by which the aerated blood received 

 from the gills is propelled through the body. The admission 

 of water to the branchia3 is effected by the expansion of the 

 mantle so as to allow the entrance of the outer water into the 

 pallial chamber. The mantle then contracts, and the water 

 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 respi- 

 ration 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-ossophageal 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 ap- 

 proach which we have yet met with, to the Vertebrate type of 

 organisation. 



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 secre- 

 ting 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 ' sperm atophores,' 

 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 serves to convey the seminal 



