382 



Glossary 



evolutionary science dealing with 

 natural propagation and devel- 

 opment, the interest centering at 

 present in that portion of devel- 

 opment which is hereditary and 

 involves sex cells. 



GERM-PLASM. Actually all the pro- 

 toplasm of the germ-cells which 

 participates in development; the- 

 oretically merely the small por- 

 tion of the germ-cells supposed 

 to be "hereditary substance." 



GONAD. A mass of undifferen- 

 tiated, generative tissue from 

 which the male and female re- 

 productive glands originate. 



GONOPHORE. The ultimate gener- 

 ative zooid of a hydrozoan, giv- 

 ing origin directly to the genera- 

 tive elements. 



HECTOCOTYLIZED. Applied to the 

 remarkably altered condition as- 

 sumed by one of the arms of the 

 male cephalopod to make it an 

 organ for impregnating the feT 

 male. 



HELIOTROPIC. Responding to the 

 stimulus of sunlight. 



HETEROMORPHOSIS. A kind of re- 

 generation in which the part pro- 

 duced is different from that 

 which was lost, as, for example, 

 when an antenna-like structure 

 grows in the place of an eye- 

 stalk, in some crustaceans when 

 the eye stalk is cut off. 



HISTOGEXESIS. The process of tis- 

 sue genesis, or production, from 

 undifferentiated cell masses, in 

 plants and animals. 



HISTOLOGY. The science of tissues, 

 plant or animal; microscopical 

 anatomy. 



HORMOXE. Literally something 

 which excites or stirs up. Orig- 

 inally and strictly applied to 

 those internal secretions (which 

 see), the office of which is to 

 incite the parts on which they 

 act to greater activity. But in- 

 ternal secretions are 'also known 

 now which retard or inhibit the 



action of the part they affect; 

 and to these it has been proposed 

 to apply the term chalone, that 

 which slackens. But some phys- 

 iologists use hormones as syn- 

 onymous with "internal secre- 

 tions." 



HOMONYMOUS. As used in this 

 book, an anatomical term refer- 

 ring to the different members of 

 a series which differ more or 

 less, but still all have the same 

 general name. Thus all the 

 pairs of appendages of a lobster 

 are homonymous, or ambulatory 

 appendages originally, although 

 used for a variety of purposes 

 now. 



HYDRAXTH. One of the bud-pro- 

 duced polyps of a hydroid col- 

 ony. 



IDIOPLASM. Literally plasm which 

 is very specially one's own. First 

 used to designate the hypothet- 

 ical part of the germ-cells which 

 is supposed to be alone respon- 

 sible for hereditary transmission. 

 Idioplasm may be regarded as 

 the historical antecedent of 

 germ-plasm (which see). 



INTERSTITIAL. Pertaining to or sit- 

 uated in an intervening space; a 

 term much used in anatomy to 

 signify within an organ. 



IXTERXAL SECRETION. The term 

 has long been used in the phys- 

 iology of the higher animals, in 

 contradistinction to "external se- 

 cretion," to designate the prod- 

 ucts of glands, like the thyroid, 

 which discharge their products 

 into the blood or lymph, instead 

 of upon the surface of the body 

 or into the digestive or some 

 other cavity of the body. The 

 existence of internal secretions 

 was known long before anything 

 was known about their use; 

 hence this non-committal name, 

 so far as function is concerned. 

 The recent discovery of their 

 office has suggested the name 



