GLOSSARY 453 



SYNAPSIS. The pairing of h^molp4 ous chromosomes during matu- 

 ration of the germ cells. 

 SYNAPTIC MATES. Homologous chromosomes of maternal and 



paternal origin paired in synapsis. 

 SYNGAMY. The union of gametes to form a zygote. 

 SYNKARYON. The composite nucleus formed by the union of the 



nuclei of two gametes. Male and female pronuclei united to 



form the fertilization nucleus. See Zygote. 

 TAPIR. A large herbivorous Mammal, having short stout limbs and 



flexible proboscis with the nostrils near the end. New World 



species are brownish-black, those of the Old World are black and 



white. 



TAXONOMY. The science of classification. 

 TELOPHASE. Final phase of mitosis during which the two daughter 



nuclei are reformed and cytoplasmic division is completed. 



See Prophase. 

 TESTIS. The definitive male reproductive organ in which the 



gametes (sperm) develop, 

 THALLUS. A relatively simple plant body, not differentiated into 



root, stem, and leaf ; e .g . , in Seaweeds and other multicellular Algae 

 THORAX. The anterior chamber of the coelom in Mammals, con- 

 taining lungs and heart. The middle portion of the body in the 



Arthropoda; e.g., in all Insects. In the Crayfish the head and 



thorax are fused to form the cephalothorax. 

 THYMUS. A glandular structure in the pharyngeal region of 



Vertebrates. Disappears during early life in Man. Function 



unknown. 

 THYROID. A glandular structure in the pharyngeal region of 



Vertebrates. Supplies an important hormone. 

 TISSUE. An aggregation of similar cells for the performance of a 



certain function. See Organ. 

 TRACHEIDS. Elongated cells which form water-conducting vessels 



in the vascular bundles of higher plants. 

 TRANSPIRATION. The exhalation of water vapor, particularly 



through the stomata of higher plants. 

 TRICHOCYSTS. Minute bodies, arranged in the outer part of the 



