GLOSSARY 



253 



Axial organ. A structure near the stone canal of echinoderms which is 

 apparently connected with genital organs. 



Basipod. Second segment from proximal end of protopod in a crus- 

 tacean appendage. 



Beak. Horny mouth parts; the point from which growth has proceeded 

 in a clam shell. Cf. Umbo. 



Bilateral symmetry. Body plan such that the organism may be cut 

 in but one plane to produce equivalent or mirror-image halves 

 (right and left). 



Biramous. Composed of two branches, as a typical crustacean appen- 

 dage. 



Bivalve. Having two valves or pieces, as a clam shell. 



Bivium. The two rays of a starfish which are nearest the madreporic 

 plate. 



Blastostyle. The reproductive zooid (probably a degenerate hydranth) 

 in certain hydroids. The gonophores (sporosacs and medusae) are 

 developed on the blastostyle. 



Body cavity. See Coelom. 



Body wall. The outer wall of the body. 



Brain. In invertebrates, frequently applied to the cerebral ganglia. 



Branchiae. Gills; organs adapted for aquatic respiration. 



Branchial heart. An accessory heart placed at the base of a gill, as in 

 the squid. 



Brood sac. A cavity or pouch in which developing embryos are carried. 



Bud. An outgrowth or ingrowth which will become a new individual. 



Byssal gland. A gland in the reduced foot of certain pelecypods, e. g., 

 Mytilus. It produces the byssal threads, collectively known as the 

 byssus. 



Byssal thread. One of the threads by which certain pelecypods attach 



themselves. 



Caecum. A blind saclike outgrowth of the alimentary canal. 



Calciferous glands. Esophageal glands of some annelids. 



Calyptoblastic. Possessing hydrothecae and gonothecae. 



Capitate tentacle. One which is enlarged or globose at its distal end. 



Carapace. The covering of the head and thorax in some crustaceans. 



Cardiac stomach. Anterior or first division of the stomach. 



Caudal cirrus. A cirrus found on the caudal end, especially of nemer- 



tines and annelids. 

 Carpopod. Third segment from proximal end of endopod in Crustacea. 

 Cellulose. The most important material in the walls of plant cells. A 



cellulose-like substance (tunicin) is found in the tunic of many 



Urochorda. 



