604 



LECTURE XXIV. 



219 



of the Animal Kingdom, but, in respect of its closer proximity to the 

 Vertebrate type, unquestionably at the head of the whole Invertebrate 

 series. 



The body of the Dibranchiate Cephalopod is divided, as in the Nau- 

 tilus, into two parts ; a head {fig. 220, A.), containing the organs of 

 sense, mastication, and deglutition, and supporting the prehensile 

 and principal organs of locomotion (c), and a trunk or abdomen (b), 

 consisting of a muscular sac or mantle, with a transverse anterior 

 aperture, and containing the respiratory, generative, and digestive 

 viscera. With the exception of the females of one genus {Ai-gonauta, 

 fig. 220.), the body is naked, includes a more or less rudimental shell, 

 and supports, in most of the species, a pair of fins. Compared with 

 the Nautilus, the cephalic appendages are much reduced in number, 

 the external ones, continued from the oral sheath, not exceeding eight 

 {fig. 219, c, c), to which, in most of the genera, is added a pair of 

 internal and much longer tentacula 

 (d, d). The arms are much in- 

 creased in size and of a more com- 

 plicated structure, supporting on 

 their internal surface numerous 

 suckers, and sometimes connected 

 togetherby a powerful muscular web. 

 The eyes are much larger and more 

 complex, are no longer peduncu- 

 lated, but lodged in orbits. The 

 mouth is armed with two piercing 

 and trenchant jaws, resembling in 

 shape and in their vertical move- 

 ments those of the Nautilus, but 

 wholly composed of horn. The 

 gills are two in number, each with 

 a ventricle appropriated to the 

 branchial circulation ; the systemic 

 circulation having a single mus- 

 cular ventricle, as in the Nautilus. 

 The infundibulum {i) is a complete 

 muscular tube, shaped like an in- 

 verted funnel. The Dibranchiates 

 possess a gland and membranous re- 

 ceptacle for secreting and expelling 

 an inky fluid. The sexual organs are 

 in distinct individuals, as in theTe- 

 trabrauchiate order. All the species of both orders of Cephalopoda 



Loligo vulgaris. 



