GLOSSARY. 



" individual " is thus regarded as including all the parts or buds 

 developed from one sexually fertilized germ, although some of 

 these buds may form apparently independent animals. 



Karyokinesis (Gk. Kdpvov, a nut, i.e. nucleus of a cell, and kiVi/o-is, 

 movement). — A name which has been given to the cycle of 

 changes which the nucleus of » cell goes through before its 

 division. See p. 21. 



Larva (Lat. larva, a. maslc). — The early stage of an animal that 

 undergoes metamorphosis : so called, because the perfect form 

 sometimes emerges from the dried skin of the early stage, which 

 hides it like a mask ; e.g. the butterfly from the dried skin of the 

 chrysalis. 



Life-History. — A complete description of the different stages of 

 any organism, from its earliest unicellular stage to its adult 

 form, is called its life-history. The life-history of an animal 

 presenting " alternation of generations," or of an animal which 

 passes through metamorphosis, is of course a long story, and 

 it is in these cases chiefly that this picturesque term is 

 applied. 



Median Line (Lat. medianus, situated in the middle, medius). — The 

 name given to the middle line of the body in animals that are 

 bilaterally symmetrical. 



iVlembrane Bone. — This term is applied to bones which are 

 derived originally from transformed scales. See p. 261- They 

 are sometimes called pabosteal bones (Gk. irapi., along-side of, 

 and iariov, bone), because they are applied on the outside of 

 the true bone. 



Mesenchyme (Gk. ixiaoi, middle, and xeC/ia, liquid). —A name given 

 to the middle layer of the body in the Gaelenterata. The name 

 refers to its jelly-like texture, which is exemplified iu ihejelly- 

 fishex, where it is enormously developed, and has been given 

 in order to allow for the doubt whether the middle layer of the 

 body in these animals is derived from the primary layers in quite 

 the same way as what is called mesoblast in the higher animals 

 such as vertebrates. 



Mesentery (Gk. /xio-os, middle, and hrepa, intestines). — 1. The thin, 

 membrane-like structures by which the intestines of vertebrates 

 are slung in their places. 2. The internal radial projections 

 of the body-wall in sea-anemones and corals. 



Mesoblast (Gk. /i^ffos, middle, and ^Xdo-Tos, germ). — The middle of 

 the three germinal layers, from which are derived the supporting 

 tissues of the body (muscles and connective tissue), and also 

 the blood. 



Metamere (Gk. /iera, after, and /x^/sos, a part). — One of the suc- 

 cessive similar joints of an articulated animal, such as a lobster. 

 A " segment." 



Metamorphosis (Gk. fiExa, and /iio/d0;), form). — Change of form; 

 when an animal passes through a larval stage before it arrives 



