300 GLOSSARY OF EMBRYOLOGICAL TERMS 



Sagittal — mesial plane, or any plane parallel to it, dividing right parts 

 of body from left. Right angles to both frontal and transverse planes. 



Sclerotic Coat — tough mesenchymatous and partially cartilaginous coat 

 outside of choroid coat of vertebrate eye. (Syn., sclera.) 



Sclerotome — loose mesenchymal cells proliferated off from inner and 

 ventral edges of myotomes (5 mm. frog) which contribute to formation 

 of axial skeleton. 



Secondary Oocyte — stage in oogenesis between primary oocyte and ovum; 

 may be either haploid or diploid, depending upon species considered. 



Secondary Spermatocyte — stage in spermatogenesis in which next division 

 results in haploid spermatids, these spermatocytes being either haploid 

 or diploid, depending upon species considered. (See Post- and Pre- 

 reduction.) 



Secretory Tubule — portion of kidney tubule actually involved in excretory 

 process. 



Section — generally a slice of an embryo, often of microscopic dimensions, 

 taken in any one of the various planes such as frontal, transverse, or 

 sagittal. (See Serial Sections.) 



Segmental Plate — See Axial Mesoderm. 



Segmentation — repetition of structural pattern; used as synonym for cleav- 

 age as well as for metamerism. 



Segmentation Cavity — cavity of blastula. (Syn., subgerminal cavity, blasto- 

 coel.) 



Semi-Circular Canals — tubular derivatives of utricle lined with ectoderm 

 from otocyst, which constitute accessory balancing mechanisms of 

 vertebrates. 



Seminal Vesicle — glandular dilation of distal end of ductus deferens 

 (Wolffian duct) where spermatozoa are temporarily collected prior to 

 ejaculation. 



Semination — act 'of fertilizing by discharge of spermatozoa. 



Seminiferous Tubule — tubular divisions of testis derived from rete cords, 

 covered by a connective tissue theca and containing supporting (Sertoli) 

 cells and all stages of spermatogenesis. 



Sense Plate — narrow band of elevated ectodermal tissue which passes 

 transversely across anterior end of amphibian embryo, ventral to level 

 of fused neural folds, with ends of band bending dorsally to merge 

 with neural folds. Lower margins represent mandibular arch, the 



