GLOSSARY. 369 



part of the blastoderm in which the embryo is developed. The 

 germinal epithelium is that part of the peritoneal lining from which 

 the generative organs take their origin. 



Gland. An organ composed of one or more epithelial cells, the physio- 

 logical function of which is secretion or excretion. The term is also 

 applied to other organs, such as the lymphatic glands, thymus, pineal 

 gland, hermaphrodite gland, etc. 



Gonad. A term applied to the reproductive organ, male (testis or 

 spermary), female (ovary) or hermaphrodite (ovotestis of snail). 



Hepatic. Of or belonging to the liver. Hepato-pancreas, a term applied 

 to the invertebrate digestive gland, as in the crayfish. 



Hermaphrodite. Combining male and female in the same organism (earth- 

 worm) or organ (ovotestis and hermaphrodite duct of snail). 



Histology. The microscopic study of tissues. Histolysis is the breaking 

 up of a tissue during development. Histogenesis is the embryological 

 development and origin of tissues. The term Histozoa has been 

 employed as equivalent to metazoa. 



Holoblastic. A term applied to segmentation, where the cleavage affects 

 the whole ovum ; opposed to meroblastic, where the cleavage is only 

 partial and restricted. 



Holometabola. See Ametabola. 



Homologous organs. See Analogous organs. 



Impregnation. The fertilisation of an ovum by the entrance of a sper- 

 matozoon. 



Ingestion. The taking in of food particles. It may be inter -cellular, 

 between the cells, or intra-cellular into the cells. 



Intus-susception. The incorporation of new material with the old during 

 life and growth ; as opposed to accretion, the addition of layer upon 

 layer. 



Invagination. The pushing in of a part of the surface to form a pouch; 

 the gastrula (e.g.] is produced by the invagination of the blastosphere 

 to form a two-layered cup. Evagination is the converse process, where 

 a pouch is pushed outwards, or where an invaginated pouch is turned 

 inside out. 



Irritability. The property of responding to a stimulus. Specialised in 

 nerve and muscle. 



Karyokinesis. A complex process undergone by the nucleus of many cells 



during division. 

 Katabolism and Katastate. See Metabolism. 



Lacunar. Having lacunae or spaces. 



Lamella. A leaf -like plate, e.g. of bone. Lamellar structure is where 

 there are a number of leaves. 

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