CErnALOPODA. 



161 



anterior ends are continuous and attaclied ; the posterior ends 

 are at first free, but eventually uniting they form the funnel 

 D s. The rudimentary gills h appear between the epipodium 

 and mantle. The alimentary canal is at first straight; (the 

 mouth being at a, the yent at h, in Fig. 35 a). The embryo 

 now grows faster in a vertical than in a longitudinal direction, 

 so that it takes on the cephalopodic 

 form. The intestine, as a consequence, 

 becomes bent upon itself; and the and 

 terior pair of arms grow over in front 

 of the head, and unite, so as eventually 

 to throw the mouth nearly into the 

 centre of the arms." (Huxley.) At a 

 later period of development (Fig. 35, d), 

 the respiratory movements are per- 

 formed by the alternate dilatation and 

 contraction of the mantle ; and the ink- 

 bag is conspicuous by the colour of its 

 contents. At the period of exclusion 

 fi-om the nidimental capsule, fine layers 

 of the shell of the young cuttle-fish 

 have been formed; but except the 

 nucleus, which is calcified, they are 

 horny and transparent. The lateral 

 fins are broader than in the mature animal. The embryo of 

 the Argonaut, as described by Kolliker, has simple conical 

 arms (1 — 4, Fig. 36) ; and indications of the funnel appear as 

 a ridge, p, on each side of the body ; v is the yolk sac ; o the 

 position of the future mouth ; e the eye ; h the gill ; and m the 

 mantle. 



rig. 36. Argonaut, embryo 

 in the egg. 



Family I. — ARGONAUTiDiE. 



Dorsal arms (of the female) webbed at the extremity, secreting 

 a sjonmetrical involuted shell. Third left arm in male hecto- 

 cotylised ; deciduous, colourless, develoj)ed in a sac. Female 

 polyandrous. Mantle supported in front by a single ridge on 

 the funnel. 



Genus Abgonauta, Lin. Argonaut, or paper sailor. 



Etymology y argonautai, sailors of the ship Argo. 

 Synonyms, ocythoe (Eafinesque). Nautilus (Aristotle and 

 Pliny). 



