GLOSSARY OF EMBRYOLOGICAL TERMS 265 



Blastopore — opening of archenteron (gastrocoel) to exterior, occluded by 

 yoliv plug in amphibian embryos; consisting of a slit-like space between 

 elevated margin of blastoderm and underlying yolk of chick egg; repre- 

 sented in amniota as primitive streak. 



Blastopore, Dorsal Lip of — region of first involution of cells in amphibian 

 gastrula; general area of the "organizer"; original gray crescent area; 

 cells which turn in beneath potential central nervous system (Am- 

 phioxus) and form roof of archenteron. (Syn., germ ring or marginal 

 zone.) 



Blastopore, Ventral Lip of — region of blastopore opposite dorsal lip; region 

 which gives rise to peristomial mesoderm of frog. (Syn., germ ring.) 



Blastula — stage in embryonic development between appearance of distinct 

 blastomeres and end of cleavage (i.e., beginning of gastrulation); a 

 stage generally possessing a primary embryonic cavity or blastocoel; 

 invariably monodermic. (See specific types under specific names.) 



Blood Islands — pre-vascular groups of mesodermal cells found in splanch- 

 nopleure, from which will arise blood vessels and corpuscles. 



Bowman's Capsule — double-walled glomerular cup associated with uri- 

 niferous tubule. 



Branchial — having to do with respiration. (Syn., gill.) 



Branchial Arch — visceral arches, beginning with third pair, which contain 

 blood vessels which (phylogenetically) have respiratory function dur- 

 ing embryonic development. Mesodermal components which support 

 those blood vessels are branchial arches. (Syn,, gill arch.) (See Visceral 

 Arches.) 



Branchial Artery — blood vessel which actually passes through gills (ex- 

 ternal or internal) of frog embryo. (Syn., gill artery.) 



Branchial Chamber — closed chamber (except for a single spiracular open- 

 ing on left side) which encloses internal gills of frog embryo. (Syn., 

 opercular or gill chamber.) 



Branchial Cleft — opening between branchial arches formed by invaginating 

 head ectoderm and evaginating pharyngeal endoderm (pouch) 

 through which water passes from pharynx to outside of frog. (Syn., 

 gill cleft or slit, some visceral clefts.) 



Branchial Groove — ectodermal invagination anterior or posterior to vis- 

 ceral arch, which joins branchial pouch to form branchial cleft, in 

 most instances. 



