GLOSSARY 255 



Collar cell. A cell provided with a protoplasmic collar; choanocyte. 



Colon. Variously applied to a portion of last part of digestive tract. 



Columella. Axis around which the spire of a gastropod shell is wound. 



Commensal. Organisms living together and usually partaking of the 

 same food. 



Commissure. In invertebrates, a nerve connecting two ganglia of a pair. 



Compound eye. An arthropod eye which is composed of many similar 

 units, called ommatidia. 



Connecting canal. The canal which joins the tube foot to the radial 

 canal of an echinoderm. 



Connective. In invertebrates, a nerve connecting two ganglia not of a 

 pair. 



Contractile vacuole. Pulsating ectoplasmic organelle present in fresh- 

 water protozoa and commonly absent in marine forms. It dis- 

 charges water and possibly excretory material. 



Copulation. Union for the purpose of transferring spermatozoa from 

 male to female. 



Cormidium. An assemblage of structures of a siphonophoran colony 

 consisting of a hydrophyllium, a gastrozooid, a dactylozooid and a 

 gonozooid. 



Coxa. Basal segment of the leg of an insect. 



Coxopod. Basal segment of the protopod in Crustacea. 



Craspedote medusa. A medusa possessing a velum. 



Crop. An enlargement of the alimentary canal for storage of food. 



Crystalline style. A transparent rod found in the alimentary canal of 

 many polecypods. 



Ctenophoral row. A row of swimming plates on a ctenophore. 



Cuticle. Nonliving external layer or protective covering. 



Cyst. A sac or pouch, e. g., as in the larval stage of tapeworms or 

 resting condition in protozoa. 



Cysticercus. A stage in the development of many tapeworms. 



Dactylopod. Terminal segment of endopod in Crustacea. 



Dactylozooid. Elongated tentacle-like zooid of a coelenterate, e. g., a 



siphonophore. 

 Denticle. Small, toothlike protuberance, as in the buccal cavity of some 



annelids. 

 Dermal branchiae. Epithelial projections from the surface of the body 



which are used for respiration in echinoderms. 

 Development, embryonic. The series of changes which lead from the 



fertilized egg to the mature animal. 

 Digestive gland. Any gland which secretes a digestive fluid. 

 Dimorphism. Two distinct forms of individuals in the colony or species. 



