xxvi GLOSSARY OF TECHNICAL TERMS 



HYDROID (Gr. vbpa, water serpent ; etSoj, form), Hydra-like. 

 HYDROTHECA (Gr. vbpa, water serpent ; #77/07, box), a cup-like 



skeletal structure containing a hydranth. 

 HYDROZOON (Gr. vbpa, water serpent ; faJov, animal), an aquatic 



animal of the group to which Hydra belongs. 

 HYPERPHALANGY (Gr. vircp, above ; c/mAayf , phalanx), a condition 



in which the number of phalanges in the digits is increased, 



as in some whales. 

 HYPERTONIC (Gr. virep, above ; roWs, tone), a term applied to 



solutions in which the osmotic pressure has been raised by 



addition of salts, &c. 

 HYPOBLAST (Gr. VTTO, below ; jQAaorJs, germ), the innermost 



layer of cells in the embryo of a multicellular animal. 

 HYPOSTOME (Gr. VTTO, below ; oro'/xa, mouth), the part below the 



mouth in a'hydroid animal. 

 ID (Gr. iSioj, personal, peculiar), a complete ancestral germ-plasm, 



. a chromomere (Weismann). 

 IDANT (Gr. iSto?, personal, peculiar), an aggregation of ids, a 



chromosome (Weismann). 

 IDIOPLASM (Gr. Ibios, personal, peculiar ; TrXdofjia, formative 



material), the hereditary substance of any particular 



cell. 

 INFLORESCENCE (L&i.florescere,io begin to flower), the arrangement 



of flowers on the parent plant. > 

 INTEGRATION (Lat. integer, entire), the process by which individuals 



of a lower order become united to form an individual of a 



higher order. 

 INTERCELLULAR (Lat. inter, between ; cellula, a small chamber 



[cell] ), lying between cells. 

 INTERCLAVICLE, one of the bones of the shoulder girdle in reptiles 



and monotremes. 



INTERSTITIAL, occupying interstices or gaps. 

 INTUSSUSCEPTION (Lat. intus, within ; suscipere, to take up), the 



addition of new particles throughout the entire mass (of 



protoplasm), resulting in growth. 

 INVAGINATION (Lat. in, in; vagina, sheath), the pushing of one 



part of a hollow body into the other, so that part of the 



original outer surface becomes internal. 

 INVERTEBRATE (Lat. in-, not ; vertebra), without a backbone. 

 ISOGAMY (Gr. 60-os, equal ; yajuo?, marriage), the conjugation of 



similar, mutually undifferentiated gametes. 



