ANIMAL KINGDOM. 



lit 



rate, and the genital organs, slow in their 

 development, are highly complicated in the 

 perfect state. These animals generally pass 

 through a series of metamorphoses, and throw 

 off their exuvial covering five or six times 

 during their development. This class is the 

 most numerous in the animal kingdom, com- 

 prehending about a hundred thousand species. 

 The greater part of their life is spent in the 

 larva state, during which they are generally most 

 voracious, like the young of other classes. In 

 the adult state the masticating organs and the 

 digestive apparatus vary much according to 

 the kind of food in the different species, as is 

 seen in comparing the alimentary canal of a 

 carnivorous cicindela campestris (Jtg> 37.) with 



Fig. 37. 



Fig. 38. 



that of a phytophagous melolontha vulgaris, 

 (fig- 38.) In the carnivorous insect (Jig. 37.) 

 the intestine passes nearly straight through the 

 body with few enlargements in its course, and 

 the glandular organs have a simpler struc- 

 ture. The oesophagus passes down narrow 

 from the head, and dilates into a wide glandu- 

 lar crop (), which is succeeded by a minute 

 gizzard, and this is followed by the chylific 

 stomach (b, c), which is covered like the crop 

 with minute glandular cryptae or follicles. At 

 the pyloric extremity of the chylific stomach, the 

 liver, in form of simple biliary ducts, pours its 

 secretion into that cavity by two orifices on each 

 side (rf). The short small intestine (e) opens into 

 a wide colon (J"\ which terminates in the anus 

 (g). In the vegetable-eating insect, (jig. 38) 

 the alimentary canal is more lengthened, con- 

 voluted, and capacious, with more numerous 

 dilatations, and the glandular organs are more 

 developed. The crop (a) of the melolontha is 



succeeded by a minute rudimentary gizzard, and 

 to this succeeds a long and sacculated glandu- 

 lar or chylific stomach, which becomes narrow 

 and convoluted below, and terminates in a 

 small pyloric dilatation, which receives the 

 four terminations of the biliary organs. The 

 succeeding part of the intestine is also con- 

 voluted, and has three enlargements in its 

 course to the anus (e). The liver (c c) is 

 here of great magnitude, and has its secreting 

 surface much extended by the development of 

 innumerable minute cceca from its primary 

 ducts. Insects also often present distinct 

 urinary organs, and numerous glands in both 

 sexes connected with the organs of generation. 

 (See INSECTA.) 



12. Arachnida, with the head and thorax 

 united, generally four pairs of legs ; with- 

 out antennae, or compound eyes, or wings, 

 or metamorphosis ; the trunk divided into a 

 cephalo-thorax and abdomen ; the head is often 

 provided with two pairs of chiliform manduca- 

 tory organs ; the eyes are simple. The respi- 

 ration is aerial, sometimes performed by tra- 

 cheae, and sometimes by pectinated pulmonary 

 sacs opening on the sides of the abdominal 

 surface of the trunk. In their nervous, res- 

 piratory, and circulating systems they indicate 

 a higher grade of development than insects, 

 and like them are generally inhabitants of the 

 land, attaining considerable size and strength, 

 with cunning, cruel, carnivorous habits, and 

 often provided with poisonous instruments. 

 (See ARACHNIDA.) 



13. Crustacea, with the head and thorax 

 generally united, two pairs of antennae, two 



