MULTICELLULAR ANIMALS 



167 



side of the thorax and are shielded by heavy chitinous plates. An- 

 terior to this narrow shed in which the gills lie is a modified leg 

 with a spoon-shaped extremity which by constant motion draws 





BAILER 



GILLS IN 

 POSITION 



GILLS PULLED DOWN 



Fig. 109. — The gills and gill chamber of a lobster. The shield that covers the gill 



chamber has been cut away. 



water through the gill chamber. In some of the members of the class 

 Arachnida, the spiders, membranous folds in sacs, arranged like 



Z./K£-/? 



INTESTINE 



ovApy 



HEART 



BOOK LUNG 



SPINNING GLANDS 



PULMONARY SAC 

 Fig. 110. — A diagrammatic long section through the abdomen of a spider to 

 show the position of the book lungs. (After Leukart, with modifications after 

 Warburton.) 



pages in a book, form what are called book lungs (Fig. no). In 

 the class Insecta, the insects, and in some spiders, an entirely differ- 

 ent type of respiratory system occurs, consisting of a set of tubules 



