GLOSSARY 195 



Ectoderm: the outermost layer of cells in the Cnidaria and Spongiaria; 



Hydra, 146; tubularians, 151; campanularians, 157. 

 Ectosarc: the outermost layer of non-granular protoplasm in protozoans; 



Paramecium, 165; Vorticella, 169; Amoeba, 174. 

 Elytra : the hard wing-covers in beetles, 5. 

 Embryo: a young animal which is passing through its developmental 



stages, usually within the egg membranes or in the maternal uterus. 

 Encyst : the act of an animal in forming a cyst about itself. 

 Endoderm : the innermost layer of cells in the Cnidaria and Spongiaria: 



Hydra, 146; tubularian, 151; campanularian, 157; sponges, 163. 

 Endopodite: the innermost of the two terminal branches of the typica, 1 



crustacean -foot ; crayfish or lobster, 26 ; sow-bug, 41; Daphnia, 50. 

 Endosarc: the inner granular protoplasm in protozoans; Paramecium, 165; 



Vorticella, 169; Amoeba; 174. 

 Endoskeleton : an internal supporting structure. 

 Endostyle: a ciliated and glandular groove in the mid-ventral line of the 



pharynx in ascideans, 127. 

 Epicranium: the sclerite forming the dorsal, median, and lateral walls of 



the head in insects, 10. 

 Epimeral plates : plates which may extend from the latero-ventral sides of 



the thorax in amphipods, 42. 

 Epiphragma: the disc of calcified slime with which a land snail can close 



the opening of its shell, 102. 

 Epipodite : a membranous projection of the protopodite ; crayfish or lobster, 



25; crab, 37. 

 Exopodite: the outermost of the two terminal branches of the typical 



crustacean foot; crayfish or lobster, 26 ; sow-bug, 41 ; Daphnia, 50. 

 Extensor muscle : a muscle that extends an organ, 31. 

 Extremity : a paired lateral or ventral appendage of the body of an animal, 



used primarily for locomotion, although in many cases having second- 

 arily some other function, 1. 

 Exumbrella : the aboral side of a medusa, 153, 159. 



Femur: the segment of an insect's leg between the trochanter and the 



tibia, 4, 10. 



Fertilization: the union of the spermatozoon and the ovum. 

 Flagellum: a vibratory thread-like projection of certain cells; hydroids, 



148, 157; sponges, 163: also of flagellate infusorians, 172. 

 Flame cell : the terminal cell of an excretory tubule of flatworms, 72. 

 Flexor muscles: a muscle that bends an organ, 31. 



