GLOSSARY 461 



synapsis the members of each pair are conjoined and interchange 



of allelomorphic genes may occur. 

 Synaptic mates. Refers to the pairs of chromosomes, carrying the same 



or alternative characters, that conjoin during synapsis. 

 Syrinx. The voice-producing apparatus of the bird. 

 Taxonomy. The science of classification. 

 Teleolecithal (Adjective). Eggs containing a relatively large quantity 



of yolk and polarized so that the greater quantity of yolk is in the 



vegetal hemisphere. 

 Telophase. An arbitrary stage in the process of mitotic cell division 



characterized by the re-formation of the nuclear membrane and 



the reorganization of the nucleus of the daughter cells. 

 Thermotropism. Response to heat. 



Thorax. The forward portion of the main part of the animal body. 

 Thrombin. An enzyme in the blood formed by prothrombin and con- 

 cerned in the conversion of fibrinogen to fibrin. 

 Tissue. An association of cells and intercellular substance in a metazoon 



or a metaphyte. The cells in a tissue are usually of the same sort. 

 Toxemia. Disease in which the disease-producing bacteria are confined 



to some organ or tissue and produce their effects on the host by 



reason of the poisonous nature of the substances formed in their 



metabolism; these poisons are absorbed by the host circulation and 



affect all other regions of the host body. 

 Toxin. A product of bacterial metabolism poisonous to its host. 

 Trachea. The tube in air-breathing vertebrates that leads air from the 



larynx toward the lungs. 

 Trachea. The fine tubules in insects and some spiders that plumb the 



air to the tissues and constitute the essentials of a respiratory tract. 

 Transmittor. As used here this term refers to tissues that conduct 



impulses. 

 Trihybrid. The progeny of a cross between two parents that differ in 



three pairs of alternative characters. 

 Triploblastic (Adjective). An animal that consists of three primary 



cell layers and their derivatives. 

 Tropism. Response that is forced by the nature of the stimulus. 

 Trypsin. A proteose-digesting enzyme of the small intestine. 

 Typhlosole. The longitudinal fold of tissue in the stomach-intestine of 



annelids. 

 Umbilical cord. A long cord that serves as the conduit containing the 



