110 



ANIMAL KINGDOM. 



around the anterior part of the body. They 

 are termed rotifera from the appearance of 

 revolving wheels produced by the rapid move- 

 ment of the cilia disposed around the mouth. 



One of these minute wheel-animalcules, the 

 hydatina senta, is represented highly magnified 

 in Jig. 35, where the mouth (a) is surrounded 

 with long vibratile cilia (b 6). The oesophagus 

 (c) leads to a capacious stomach (</), which 

 becomes a narrow intestine below, opening 

 into the cloaca (e), where the genital organs 

 (i,i,g,g,h,) also terminate. Several ganglia 

 surround the oesophagus, and a dorsal vessel 

 (o o) is seen extending along the middle of the 

 back and sending out regular transverse 

 branches. All the rotifera are free, most are 

 naked, many are sheathed or loricated, they 

 exhibit no branchial or pulmonary organs, they 

 are remarkable for their fertility and their 

 tenacity of life. (See ROTIFERA.) 



8. Cirrhopoda, aquatic, articulated, diplo- 

 neurose animals, with articulated cirrhi, and 

 branchiae for respiration, body covered with 

 a fleshy mantle, and fixed in a multivalve 

 shell. These animals are all marine, the 

 branchiae are fixed to the bases of the articu- 



lated cirrhi, the mouth is provided with man- 

 dibles and maxillae, there is a pulsating dorsal 

 vessel, and a double longitudinal knotted sub- 

 abdominal nervous chord. The cirrhopoda have 

 been commonly placed among the molluscous 

 classes from the form of their exterior coverings. 

 (See CIRRHOPODA.) 



9. Annelida, with a long cylindrical body 

 generally divided into transverse segments, and 

 covered with a soft skin; the head commonly 

 provided with antennae and numerous simple 

 eyes, and the mouth with maxillae ; the organs 

 of motion in the form of simple setae or cirrhi 

 extending from the sides of the body in a sin- 

 gle or double row. The vascular system of 

 the annelida consists of arteries and veins, 

 without a distinct auricle or ventricle, and the 

 blood is generally of a red colour. The re- 

 spiratory organs are generally in form of external 

 branchiae, sometimes of internal air-sacs, and 

 the alimentary canal passes straight through 

 the body with two terminal openings, and with 

 numerous lateral cceca developed in its course, 

 as seen in that of the leech, kirudo medicinalis, 

 Fig. 36. (fig. 36.) These lateral cceca (b, 

 c, d, e,J', g, h, i, k, m,) increasing 

 in length and size from before 

 backwards, are often much more 

 lengthened and divided, as in the 

 halithea. Many of the red- 

 blooded worms are fixed in cal- 

 careous, arenaceous, or other 

 tubes, and many are free and 

 naked. (See ANNELIDA.) 



1 0. Myriapoda, with a length- 

 ened articulated body equally 

 developed throughout ; the head 

 provided with antennae and sim- 

 ple eyes ; the segments of the 

 trunk free, without distinction 

 of thorax and abdomen; the 

 segments furnished with one 

 or two pairs of articulated legs 

 adapted for progressive motion on land ; the 

 respiration is aerial, and performed by tracheae, 

 which ramify from their commencement in 

 stigmata which open along the whole extent 

 of the body. They do not undergo me- 

 tarmorphosis, nor possess compound eyes nor 

 wings, and they have always more than six 

 pairs of feet. (See MYRIAPODA.) 



1 1 . Insecta, with six articulated legs extend- 

 ing from an articulated trunk, which is divided 

 into a head, thorax, and abdomen; the head is 

 provided with a labium, a labrum, mandibles, 

 and maxillae, with compound and often also 

 with simple eyes, and a pair of antennae and 

 palpi ; the thorax supports the six legs, and 

 commonly one or two pairs of wings, and has 

 attached to it the moveable segments of the 

 abdomen, which embrace the principal organs 

 of digestion, circulation, and generation. The 

 respiration is effected by tracheae, which form 

 continuous lateral trunks before they ramify 

 through the body. The circulation is aided by 

 a pulsating dorsal vessel provided with nu- 

 merous valves, and the alimentary canal is 

 furnished with salivary and hepatic, and often 

 with pancreatic glands. The sexes are sepa- 



