GLOSSARY 487 



young are free-swimming, and are provided with eyes and antennas : 

 e.g. Argulus. 



Eryops : a genus of extinct amphibia belonging to the order Stegocephala. 



Eucone eyes (Gr. eu, well, complete ; konos, cone) : invertebrate eyes in which 

 the crystalline cones are well developed, as in many of the compound 

 eyes of Crustacea. 



Euphausia pellucida (Gr. eu, well ; phausis, bright ; L. pelhicidus, clear, trans- 

 parent) : an order of the Eucarida. The carapace coalesces with the 

 thoracic segments to form a continuous shield and there are stalked eyes. 



Eurypterus (Gr. eurus, wide ; pteron, wing) : an extinct scorpion-like genus 

 belonging to the order Merostoma. 



Exochrome cells (Gr. ex, out of; chroma, colour) : pigment cells of the retina 

 of extraneous origin, and thought to be derived from the subepidermal 

 connective tissue. 



Flabellum (L. flabelhim, fan) : the last appendage of the prosoma of the adult 

 Limulus has an outer segment which is called the epipodite or flabellum. 



Fluke : an internal parasitic worm of leaf-like form (Distoma hepaticum) 

 belonging to the class Trematoda. It is frequently found in the gall 

 bladder or bile ducts of the sheep. 



Fundulus heteroclitus (L. fundulus, closed end of gut, or tube ; Gr. hetero- 

 clitos, irregularly bent) : a marine minnow, the developing embryos of 

 which were used by Stockard and others for the experimental production 

 of cyclops and other deformities. 



Fuscin (L. foscus, brown) : the colouring material contained in the pigment 

 granules of the hexagonal cells of the retina, a form of melanin. 



Galeodes : an Arachnid belonging to the order Solpugidae, and resembling 

 the scorpions. 



Gammarus ornatus : the gadfly, belonging to the order Hymenoptera of the 

 class Insecta. A small median or frontal ocellus is situated between two 

 large faceted eyes. 



Ganoid (Gr. ganos, sheen ; eidos, like) : (1) A term applied to the glistening 

 scales or plates of certain fishes ; they are composed of a deep layer 

 of true bone, which is covered by a superficial layer of enamel or ganoin. 

 (2) An order of fishes characterized by incomplete ossification of the 

 endoskeleton, and an exoskeleton usually formed of rhombic, ganoid 

 plates, e.g. Polypterus ; Osteolepis, a primitive extinct genus. 



Gasteropoda (Gr. gaster, stomach ; pous, foot) : the class of Mollusca, com- 

 prising univalve forms in which movement is effected by contractions 

 of the foot — e.g. snails and slugs. 



Gastrula (Gr. gaster, stomach) : the name applied to the double-layered 

 vesicle formed by the invagination of one part of the wall of the blasto- 

 cyst into the opposite part. 



Glabella (L. glabella, smooth, bare area) : e.g. the smooth median part of the 

 cephalic-shield of a trilobite. 



Gnathostomata (Gr. gnathos, jaw ; stoma, mouth) : the Branch of fishes 

 characterized by the presence of jaws in the mouth, as contrasted with 

 the cyclostomata in which jaws are absent. 



