190 GLOSSARY 



Cilia: hair-like, motile cytoplasmic processes. 



Cleavage: the division of the egg into a number of cells by a process 



of cellular division, which is not accompanied by cell growth. 

 Cortex: outer layer. 

 Cortical: pertaining to the cortex. 



Cranial: pertaining to or directed towards the head. Opp.: caudal. 

 Cumulus oophorus: the follicle cells surrounding the egg in the 



follicle of the mammalian ovary. 

 Cyclopia: abnormality, in which only one median eye is present. 

 Cy taster: aster formed at an arbitrary place in the cytoplasm. 

 Cytology: the science of cells. 

 Cytoplasm: protoplasm of the cell, as opposed to that of the nucleus 



(cf. nucleoplasm). 

 De-differentiation: reduction in the differentiation that has already 



taken place. 

 Depolarlsation: loss or reduction of polarity. 



Determinants: material particles, regarded as the carriers of in- 

 heritable properties. Cf. genes. 

 Determination: the fixation of the course of future development in 



a part of the germ. 

 Differentiation: the division of a whole into recognisable parts; the 



appearance of differences among originally identical parts. 

 Diploid: containing a double set of chromosomes. This is the usual 



condition in the majority of the cells of the body. Cf. haploid, 



polyploid. 

 Dispermy: Fertilisation by two sperms. Cf. monospermy, polyspermy. 

 Double-monster: organism formed by two individuals grown to- 

 gether. 

 Ectoderm: outer germ-layer, the outer cell -layer of the gastrula. 



Cf. mesoderm, endoderm. 

 Ectoplasm: outer layer of the cytoplasm; also, protoplasm which 



will later be located in the ectoderm cells. Opp.: endoplasm. 

 Embryogenesis : the development of the embryo from the egg. 

 Enchylema: the more liquid part of the protoplasm. 

 Endoderm: inner germ-layer, inner cell-layer of the gastrula. Cf. 



ectoderm, mesoderm. 

 Endoplasm: the central part of the cytoplasm, or: the protoplasm 



that will later be located in the endoderm cells. Opp.: ectoplasm. 

 Endothelium: the tissue lining cavities in the body, such as blood 



and lymph vessels. 

 Entelechy: a hypothetical, purposive vital force. 

 Enzyme: organic substance with the properties of a catalyst; =■ 



ferment. 

 Epigenesis: the appearance of new structures in the course of 



development. 

 Epithelium: tissue, consisting of a sheet of closely packed cells, 



covering an internal or external surface of the body. Cf. endo- 

 thelium. 



