GLOSSARY 



477 



ENDODERM - the innermost layer of the dider- 

 mic gastrula. Arises from the vegetal 

 hemisphere of amphibia. Syn. , entoderm. 



ENDODERMISATION - shifting of an animal- 

 vegetal gradient of an egg toward the veg- 

 etal gradient, causing hyper-development 

 of the endodermal structures. Can be 

 brought about by physical, chemical, or 

 surgical means. 



ENDOPLASM - inner medullary substance of 

 the egg cell which is generally granular, 

 soft, watery, and less refractory than the 

 ectoplasm. Surrounded by ectoplasm. 



ENDYSIS - the development of a new cuticular 

 covering, opposed to ecdysis. 



ENTELECHY - Driesch's theory of harmonious, 

 equipotential system suggested an agent 

 controlling development which he termed 

 "elan vital". An intensive manifoldness; 

 the intangible controlling order of develop- 

 ment ("intensive Mannigfaltigkeit" of 

 Driesch). 



ENTOMESOBLAST - cell which will give rise 

 to the trunk mesoderm in the determinate 

 type of cleavage characteristic of annelids. 



ENTO-MESODERM - refers to that portion of 

 the invaginating blastoporal lips which will 

 induce the formation of medullary fields 

 in the amphibia. 



ENTOPIC - in the normal position, opposed to 

 ectopic (referring to transplants). 



ENTRANCE CONE - the temporary depression 

 on the surface of the egg following the en- 

 trance of the spermatozoon. 



ENTRANCE PATH - (See path, entrance or 

 penetration) 



ENTWICKLUNGSMECHANIK - causal embry- 

 ology (Roux); the seat and effective dura- 

 tion of the morphogenetic forces which are 

 explored, by microsurgical means, and 

 which seem to be responsible for the devel- 

 opment of embryonic segregation (Lehmann, 

 1942). 



ENTWICKLUNGSPOTENZEN - the total accom- 

 plishment of a blastema, experimentally 

 determined (Raven). 



EPIBOLY - growing, spreading, or flowing 

 over; surrounding of inner masses (yolk 

 and/or cells) by overgrowing ectoderm; 

 process by which the rapidly dividing ani- 

 mal pole cells (often micromeres) grow over 

 and enclose the vegetal hemisphere mate- 

 rial. Increase in areal extent of the ecto- 

 derm. (Simile: rubber cap being pulled 

 down over grapefruit. ) 



EPIGAMIC - tending to attract the opposite sex. 



EPIGENESIS - developing of systems starting 



with primitive, homogeneous, lowly organ- 

 ized condition and achieving great diversifi- 

 cation. Term coined by Harvey, the anti- 

 thesis of preformation. 



EPIGNATHUS - union upon the jaw of parasitic 

 growth. 



EPIMORPHOSIS - proliferation of material pre- 

 cedes the development of new parts. 



ERGASTOPLASM - basophilic parts of the cyto- 

 plasm, mitochondria of cytologists. 



ERRERA'S LAW - "a cellular membrane at the 

 moment of its formation tends to assume 

 the form which would be assumed under the 

 same conditions by an elastic membrane 

 destitute of weight" (Gray, 1931). 



ESTROGEN - secretion product of the ovary which 

 controls oestrus and endometrial growth. 



ESTROUS CYCLE - the periodic series of 



changes which occur in the mammalian uter- 

 us, related to the preparation of the uterus 

 for implantation of the ovum, and to repair. 



ESTRUS - period of the reproductive cycle of 

 the mammal when the uterus is prepared 

 for implantation of the ovum. 



ETHEOGENESIS - development of the sperma- 

 tozoon without fertilization; male partheno- 

 genesis. 



EUCHROMATIN - the part of the regular chro- 

 matic structure of the nucleus which is rich 

 in thymonucleic acid, and presumably the 

 genes, alternating (in the chromosomes) 

 with achromatic regions. It is in the form 

 of discs, and takes methyl green stain. 



EUPLOIDY - deviation from the normal diploid 

 condition but involving complete sets of 

 chromosomes (Tackholm, 1922). 



EUTELY - constancy of cell numbers in the 



various organs of plants and animals, more 

 dependable in animals than in plants (Wett- 

 stein, 1927, Heilborn, 1934). 



EVAGINATION - the growth from any surface 

 outward. 



EVOCATION - mere calling forth of potential- 

 ities through contact; non-assimilative in- 

 duction, no organization except that which 

 is present within the host material; that 

 portion of the inductive response which can 

 be achieved by killed, crushed, or narco- 

 tized organizers of any level. 



EVOCATOR - a chemical substance which has 

 the power of calling forth the latent poten- 

 tialities of an embryonic area; a morpho- 

 genetic stimulus. 



EXCLUSIVITY - discreteness of the differentia- 

 tion process (Weiss). 



EXGENITO-VIVIPARITY - the embryo in a 



stage of development which corresponds to 

 the egg stage of ovoviviparous forms, ob- 

 tains its nourishment by means of a tro- 

 phamnion, trophoserosa or trophochorion. 

 Development occurs in the haemocoele, not 

 in the uterus (e. g. , Strepsystera). 



EXOGASTRULA - gastrulation modified exper- 

 imentally by abnormal conditions so that 

 invagination is partially hindered and there 

 remains some mesendoderm not enclosed 

 by ectoderm; evagination of the primary 

 intestinal cavity, or archenteron. (See 

 vegetativisation. ) 



