192 GLOSSARY 



Histog-enesis : the origin of tissues. 



Homospermic merogony: development of a non-nucleated egg 

 fragment after fertilisation by a sperm of the same species. 

 Opp.: heterospermic merogony. 



Homozygote: organism arising from a zygote formed by the fusion 

 of gametes that were identical as regards the gene under 

 consideration. Opp.: heterozygote. 



Hormones: substances secreted in definite parts of the body, under 

 the influence of which certain processes take place in other 

 parts of the body to which they are carried by the blood. 



Hybrid: individual arising from a cross between two races or species. 



Hypertrophy: excessive growth by the increase in size of tissue 

 elements. 



Implantation: the grafting of a cell group or organ into an abnor- 

 mal place, in particular into one of the body cavities. Cf. ex- 

 plantation, transplantation. 



Induction: the influence exerted by an inductor. 



Inductor: cell group which causes other cells to develop into a 

 certain direction. 



Intensive multiplicity: A complexity of structure which is not based 

 on recognisable regional differences in form or nature within 

 the organism or cell. Opp.: extensive multiplicity. 



Malpighian tubes: excretory organs of insects, opening into the 

 hind gut. 



Matrocline : in which the maternal characteristics dominate over 

 the paternal ones. Opp.: patrocline. 



Median plane: plane of symmetry of a bilaterally symmetrical 

 organism. 



Melanophore: black pigment cell. 



Meridian plane: plane containing both poles. 



Merogony: development of a fertilised fragment of an egg in which 

 no female pronucleus is present. 



Mesenchyme: embryonic connective tissue. 



Mesoderm: middle germ-layer, middle cell-layer of the gastrula. 

 Cf. ectoderm, endoderm. 



Mesoplasm: cytoplasm that will later become located in the meso- 

 derm cells. Cf. ectoplasm, endoplasm. 



Microdissection: operations on cells under the microscope. 



Micromeres: small cleavage cells. 



Microsomes: very small granules in the cytoplasm. 



Mitochondria: larger, rod-shaped or granular corpuscles in the cell 

 cytoplasm. 



Mitosis: indirect nuclear division. 



Modulation: change in the external appearance of cells, caused by 

 external circumstances, and not accompanied by a simultaneous 

 change in potencies. 



Monaster: simple radiation in the cytoplasm, in the centre of 

 which the chromosomes are located. Cf. amphiaster. 



