GLOSSARY 211 
Ductus ejaculatorius: the terminal portion of the male reproductive tract in 
insects, 17. 
Ectoderm: the outermost layer of cells in the Cnidaria and Spongiaria; 
Hydra, 160; tubularians, 165; campanularians, 171. 
Ectosarc: the outermost layer of non-granular protoplasm in protozoans; 
Paramecium, 185; Vorticella, 189; Amoeba, 194. 
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. 
Endopodite: the innermost of the two terminal branches of the typical 
crustacean foot; crayfish or lobster, 832; sow-bug, 47; Daphnia, 56. 
Endoskeleton: an internal supporting structure. 
Endostyle: a ciliated and glandular groove in the mid-ventral line of the 
pharynx in ascidians, 137. 
Entoderm: the innermost layer of cells in the Cnidaria and Spongiaria; 
Hydra, 160; tubularian, 165 ; campanularian, 171; sponges, 183. 
Entosarc: the inner granular protoplasm in protozoans; Paramecium, 185; 
Vorticella, 189; Amoeba, 194. 
Epicranium: the sclerite forming the dorsal, median, and lateral walls of 
the head in insects, 12. 
Epigynum: a cuticular plate covering or accompanying the female genital 
pore in many species of spiders, 26. 
Epimeral plates: plates which may extend from the latero-ventral sides of 
the thorax in amphipods, 48. 
Epiphragma: the disc of calcified slime with which a land snail can close 
the opening of its shell, 112. 
Epipodite : a membranous projection of the protopodite; crayfish or lobster, 
81; crab, 43. 
Exopodite: the outermost of the two terminal branches of the typical 
crustacean foot; crayfish or lobster, 32; sow-bug, 47; Daphnia, 56. 
Extensor muscle: a muscle that extends an organ, 33. 
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, 167, 173, 175. 
Femur: the segment of an insect’s or a spider’s leg between the trochanter 
and the tibia, 4, 12, 25. 
