GLOSSARY 377 



Cell, a minute portion of protoplasm containing a nucleus. 



Cerci (Gr. = tails), the appendages of the last abdominal segment. 



Chiasma (Gr. =a crossing, from the letter ^), a diagonal intercrossing of 

 two sets of nerve -fibres. 



Chitin (Gr. ^moi/, a tunic), the transparent horn-like substance which 

 forms the cuticle of insects. 



Chromatin (Gr. xP&>M a > colour), the substance forming the intra-nuclear 

 fibres of the cell-nucleus (so called owing to its affinity for basic stains, such 

 as haematoxylin). 



Coelome (Gr. /coiXw/xa, a hollow), in the Arthropoda, the body-cavity 

 formed by fusion of the cavities of the mesodermal somites of the embryo ; 

 in the Insecta, it is much reduced. In some other Phyla, the coelome may 

 have a different derivation. 



Commissure (Lat. commissura, a connection), a cord of nerve-fibres con- 

 necting two ganglia. 



Convergence, the term applied to indicate resemblance between two forms 

 (either of animals or structures) derived from two widely different ancestries. 

 The convergence may be due to the adoption of similar habits, or to the 

 elimination, by reduction, of the original differences. 



Corduliform (Gr. Kop8v\r), a club), shaped like an Indian club (e.g. abdomen 

 of certain Dragonflies). 



Cornea (Lat. = horny), the outer covering of the eye (in Insects, continuous 

 with the chitinous cuticle). 



Cuticle (Lat. = the skin), the hard outer non-cellular covering of Insects; 

 formed of chitin. 



Cytoplasm (Gr. KVTOS, cell ; ir\a<rpa, anything moulded), all the protoplasm 

 of the cell, except the nucleus. 



Dendritic (Gr. 8tv8pov, a tree), with complex branchings, like those of a 

 tree. 



Diaphragm (Gr. =a partition-wall), a membrane dividing the body-cavity 

 into two. 



Dichotomy (Gr. fa^oro/ilo, to cut in two), a phylogenetic term indicating 

 the branching of a single ancestral line into two equal and diverging lines 

 of descent. 



Dioptit or dioptric (Gr. SIOITTIKOS, fit to look through, or SionrpiKos, 

 pertaining to an optical instrument), used of the part of the eye concerned 

 with the passage and focussing of the light-rays. 



Ecdysis (Gr. K8vw, to strip off), the periodical casting of the larval skin. 



Ectoderm, see Germinal Layers. 



Efferent (Lat. = carrying outwards), a vessel conveying air or blood outwards 

 from a gill. 



Embryo (Gr. fpftpvov, the young before birth), the young animal within the 

 egg- 



Endoderm, see Germinal Layers. 



Endoskeleton (Gr. fv8ov, within), the internal skeleton. 



