164 GENERAL BIOLOGY 



anterior. At or toward the front or head end. 



anus. The posterior opening of the digestive tube. 



aorta. In invertebrates the chief artery of the body; in 



vertebrates the large artery supplying the main organs 



of the body, 

 aortic arch. The arch or loop of the main arteries as they 



leave the heart, 

 apopyle. In the sponge the opening of a radial canal into 



the central cavity. 



appendage. A subordinate part of an organ or body; es- 

 pecially an external organ or limb. 



artery. A bloodvessel carrying blood away from the heart, 

 asexual. Non-sexual; reproduction by means other than 



sexual, as by budding or fission, 

 aster. Star. The star-like structure found at the end of 



the spindle during mitotic division of the nucleus, 

 asymmetry. Lack of symmetry, especially absence of bilateral 



symmetry. 



B 



bacillus. A little staff. A rod-shaped bacterium. 



barb. A hook or point extending backward, which pre- 

 vents the pulling out of the object. 



bilateral symmetry. Symmetrical with respect to the right 

 and left sides. 



biramous. Having two branches, as a typical crustacean 

 appendage. 



bivalve. Shell composed of two lateral valves or pieces -as 

 the shell of the clam. 



blastopore. The pore opening into the primitive gut of. a 

 developing animal. 



blastostyle. That portion of the fleshy axis which pro- 

 duces medusae in certain hydroids. 



