304 GLOSSARY OF EMBRYOLOGICAL TERMS 



neural crests, to organize as a chain of ganglia near dorsal aorta and 

 controlling involuntary (visceral) musculature. 



Synapsis — union, such as the lateral (parasynapsis) or terminal (telosynap- 

 sis) union of embryos; or pairing of homologous chromosomes. 



Synaptene Stage — stage in maturation between leptotene and synizesis (con- 

 traction) stage wherein chromatin is in form of long threads, inter- 

 twined in homologous pairs. (Syn., zygotene, amphitene.) 



Syncytium — nuclei and cytoplasm without cellular boundaries; multinu- 

 cleate protoplasm without cell boundaries. 



Syngamy — specifically the fusion of the gamete pronuclei, but also the 

 union of gametes at fertilization. (Syn., zygotogenesis, fertilization.) 



Synizesis — stage in maturation between synaptene and pachytene when 

 chromatin threads are short and thick and ends away from centrosome 

 are tangled. 



Telencephalon — portion of forebrain (ventricle) anterior to a plane which 

 includes posterior side of choroid plexus and anterior side of optic 

 recess of 5 mm. frog embryo. Gives rise to torus transversus (anterior 

 commissure), cerebral hemispheres, corpora striata, anterior choroid 

 plexus, olfactory lobes, lateral ventricles, and part of foramina of 

 Monro. 



Telobiosis — fusion of embryos end-to-end. (Syn., parabiosis.) 



Telocoel — cavity of telencephalon. 



Telolecithal — See Egg, telolecithal. 



Telophase — last phase in mitosis when respective chromosome groups 

 have reached their respective astral centers and are beginning to re- 

 form a resting cell nucleus; stage often accompanied by beginning of 

 cytoplasmic division. 



Telosynapsis — end-to-end fusion of chromosomes. (Syn., parasynapsis.) 



Teratology — study of causes of monster formation. 



Tetrads — paired (homologous) chromosomes which have become dupli- 

 cated longitudinally in anticipation of the meiotic (reductional) divi- 

 sion. When viewed from end will appear as a group of four chromo- 

 somes, hence a tetrad. 



Thalamus — dorso-lateral wall of diencephalon which becomes thickened 

 by development of fibers passing from cord to more posterior parts 

 of cerebral hemispheres. 



