Glossary or Emtryolo^ical Terms 



Acidophil — oxyphil: cell constituents which stain with acid dyes, often used 

 to designate an entire cell type. (See Basophil.) 



Acrosome — apical organ at tip of mature spermatozoon, derived from 

 spermatosphere (idiosome or centrosome) and presumably functional 

 in aiding penetration of egg cortex by spermatozoon during fertiliza- 

 tion. (Syn., perforatorium.) 



Activation — process of initiating development in egg, normally achieved by 

 spermatozoon of same species but also accomplished artificially 

 (parthenogenesis); term also used to refer to stimulation of sper- 

 matozoon to accelerated activity by chemical (fertilizin) means. 



Adnexa — extra-embryonic structures (e.g., yolk sac) discarded before 

 adult condition is attained. 



Aestivation — reduced activity of some animals during heat of summer. 

 Opposed to hibernation. 



Agglutination — cluster formation; a spontaneously reversible reaction of 

 spermatozoa to certain chemical situations (e.g., egg water). 



Aggregation — coming together of cells, such as spermatozoa, without stick- 

 ing; a non-reversible response comparable to chemotropism. 



Albuginea of Testis — stroma of primitive testis which forms a layer between 

 germinal epithelium and seminiferous tubules. 



Albumen — protein substance secreted by walls of oviducts around egg of 

 reptiles and birds. 



Albumen Sac — 2-layered ectodermal sac enclosing albumen of chick egg 

 during early development of embryo, separated for a time from yolk 

 by vitelline membrane; later to release some of its contents into amni- 

 otic cavity through ruptured sero-amniotic connection. 



Amitosis — direct nuclear division without chromosomal rearrangements; 

 generally thought to be a sign of decadence or of high specialization, 

 if it occurs at all. 



*A supplementary list of some 350 specialized terms may be found in the author's 

 "Experimental Embryology, a Manual of Techniques and Procedures," Minneapolis, 

 Minn., Burgess Publishing Co., 1948. 



261 



