Vlll EXPLANATION OF THE FIGURES. 



FIG. 



67. Skull of a tiger, showing the muscles for mastication. 



68. Head of a snapping-turtle (Emysaimts serpentina) . 



69. Head of a "Whale, showing the whalebone. 



70. Head of an ant-eater. 



71. Head of an alligator. 



72. Head of a skate-fish (Myliobatis'), showing the palate bone. 



73. Head of a monkey, showing the three different kinds of teeth. 



74. Teeth of an insectivorous animal, the mole. 



75. Teeth of a carnivorous animal, the tiger. 



76. Teeth of a rodent. 



77. A polyp ( Tubularia indivisa) ; m> mouth ; 0, ovaries ; p^ tentacles. 



78. Blood globules in man, magnified. 



79. " in birds, 



80. " " in reptiles, " 



81. " " in fishes, " 



82. Portion of a vein opened, to show the valves. 



83. Network of capillary vessels. 



84. Dorsal vessel of an insect, with its valves. 



85. Cavities of the heart of mammals and birds. 



86. " " of a reptile. 



87. " of a fish. 



88. Heart and blood vessels of a gasteropod mollusk (Natica). 



89. Tracheae, or air tubes of an insect ; s, stigmata ; t } trachea. 



90. Relative position of the heart and lungs in man. 



91. Respiratory organs of a naked mollusk (Polycera iUuminata). 



92. Respiratory organs (gills) of a fish. 



93. Vesicles and canals of the salivary glands. 



94. Section of the skin, magnified, to show the sweat glands ; a, the leather ; 



b, blood-layer ; f, epidermis ; g, gland imbedded in the fat-layer (f), 



95. Egg of a skate-fish (Myliobatis') . 



96. Egg of hydra. 



97. Egg of snow-flea (Podurella). 



98. Section of an ovarian egg ; d, germinative dot ; g-, germinative vesicle ; 



s, shell-membrane ; v : vitelline membrane. 



99. Egg cases of Pyrula. t 



100. Monoculus bearing its eggs, a a. < 



101. Section of a bird's egg ; #, albumen ; c, chalaza ; e, embryo; s, shell ; 



y, yolk. 



102. Cell-layer of the germ. 



103. Separation of the cell-layer into three layers ; s, serous or nervous layer ; 



m, mucous or vegetative layer ; v, vascular or blood-layer. 



104. Embryo of a crab, showing its incipient rings. 



105. Embryo of a vertebrate, showing the dorsal furrow. 



