92 LABORATORY DIRECTIONS 



Stipple A method of portraying structure by the use of fine 

 dots. 



Succeed (See succession.) 



Succession A term used in ecology to indicate the change in 

 species present at any one point due to changes produced by 

 organisms there or due to physiographic causes. 



Symmetrical Parts of the body arranged in regular order with 

 reference to one or more axes or planes. 



Tarsal claws One or more claws or hooks at the end of an in- 

 sect's foot. 



Tarsus (pi. tarsi) : the foot. 



Thorax In arthropods and vertebrates that part of the body 

 between the head and abdomen, usually bearing appendages. 



Tissue A group of similarly differentiated cells. 



Tracheae Air tubes within the body of an insect, serving for 

 respiration. 



Transverse section A section taken at right angles to the main 

 axis of the body. 



Umbo The protuberance of a bivalve shell above the hinge liga- 

 ment. 



Ventral "The under side of the body;" or more strictly that 

 part of the body directed toward the surface upon which the 

 animal walks or comes to rest. 



Vertical section A section running from dorsal to ventral sur- 

 face through the main or chief axis of the body. 



Vestigial Any organ or structure which never reaches full de- 

 velopment and is consequently without function. 



Wing-pads Rudimentary, sac-like wings oh the thorax of many 

 nymphs. 



Zooid One of the individuals in a united colony of animals. 

 Zygote A single cell resulting from the fusion of two gametes. 



