CHAMBERS'S INFORMATION FOR THE PEOPLE. 



CLASS VII. CEPHALOPODA. 



The Cephalopoda are so named from having 

 their limps arranged in immediate connection 

 with their head. These limbs are eight or 

 ten in number, and perform all the functions of 

 feet, arms, and feelers. The body is inclosed 

 within a muscular mantle-sac. Through the ante- 

 rior tubular orifice (' funnel 0, the effete matter of 

 respiration is expelled. They are the most highly 

 organised of invertebrate animals, presenting rudi- 

 ments of an internal skeleton. The eyes are well 

 developed, and, in most of the existing species, 

 organs of hearing are present. The head is large 

 and conspicuous. They possess distinct hearts 

 for the systemic and pulmonary circulations, and 

 highly complicated nervous, digestive, secretory, 

 and respiratory organs, which are in the form of 

 two or four plume-like gills, situated within the 

 mantle. They are all marine and carnivorous. 

 ORDER I. The Dibranchiata are specially 

 suited for swimming rapidly 

 through the water. These 

 animals have two gills and 

 three distinct hearts ; an ink- 

 sac for secreting and emitting 

 an inky fluid ; and the arms 

 never above ten in number, 

 and supporting suckers. The 

 funnel is a complete tube, and 

 the shell is internal, or, if 

 external, it is not chambered. 

 The Cuttle-fish are the most 

 typical members of this order. 

 They swim backwards by 

 means of the jet of water 

 expelled through the funnel, 

 and by means of their arms 

 and suckers they creep on the 

 bottom of the sea, and retain 

 a forcible hold of their prey. This order is divided 

 into two sections, characterised by the number 

 of their arms. 



Section i. Octopodidaa are distinguished by the 



Cuttle-fish. 



Argonaut. 



possession of eight arms. They are very voracious 

 animals, and to this family belongs the Poulpe 



{Octopus) of the Mediterranean, whose shell is 

 placed internally. It is eaten as a regular article 

 of diet in the south of Europe. In the Paper 

 Nautilus (Argonauta), the female alone is pro- 

 tected by a very delicate and beautiful external 

 non-chambered shell. The male argonaut is only 

 about one inch in length. 



Section 2. The Decapoda have ten arms, two of 

 which are longer than the others (tentacles), of 

 a rounded form, and club-shaped at the extremity. 

 The suckers are placed on stalks, and the body has 

 a fin-like organ on each side ; further, the shell is 

 always internal. It includes the Calamaria, or 

 Squids for example, Loligo, the shell of which is 

 horny, and is called the 'cuttle-fish pen.' The 

 common British species (L, vulgaris) is used as 

 bait by the fishermen, and is often cast upon the 

 shores in great quantity after high winds. In 

 Sepia, the shell is calcareous, and is called ' cuttle- 

 bone/ and was formerly used in medicine. This 

 section also includes the extinct Belemnites, or 

 Jove's Thunderbolt 



ORDER 2. The Tetrabranchiata have four 

 gills, and are protected by an external chambered 

 shell with simple partitions or septa, perforated 

 by a tube or siphuncle. The last chamber of the 

 shell is the largest, and contains the body of the 

 animal. There is no ink-sac. The arms are 

 numerous, and devoid of suckers. It consists of 

 only one living family, the Nautilida, of which 

 the Pearly Nautilus (Nautilus pompilius), which 

 inhabits the tropical seas, is the type. The shell 

 of N. pompilius is partitioned off by septa into 

 chambers which gradually in- 

 crease in size towards the 

 mouth of the shell, where the 

 largest chamber is left for the 

 habitation of the animal, while 

 the other chambers are filled 

 with air. The septa are per- 

 forated in the centre by aper- 

 tures, through which there 

 passes a vincula siphuncle, 

 communicating with the cham- 

 ber where the heart is placed. 

 This order was abundantly re- 

 presented in past time by such 

 genera as Ammonites, Orthoceras, and Ceratites r 

 which are now entirely extinct. 



In the Dibranchiata, the mode of reproduction 

 is peculiar. The sexes are distinct. One of the 

 arms of the male enlarges, becomes cystic, and 

 spermatozoa are developed in its interior. Thus 

 changed, it is said to be hectocotylised. It is 

 then detached, and swims about, ultimately burst- 

 ing, and depositing the spermatic fluid within the 

 pallial chamber of the female. 



Ceratites nodosus. 



VI. SUB-KINGDOM VERTEBRATA. 



The last and highest division of the Animal' 

 Kingdom is composed of animals which have 

 their segments arranged along a longitudinal axis, 

 and exhibit bilateral symmetry. The fundamental 

 character of vertebrates is the possession of an 

 internal central axial structure called the spine or 

 vertebral column; hence the name of the sub- 

 kingdom. This structure may be bony or carti- 

 laginous, or both, and it shuts off the nervous 



