380 . GLOSSARY 



Proctodaeum (Gr. irpcaKTus, anus ; 686s, entrance), a posterior invagination 

 of the ectoderm, giving rise to the anus and hind-gut. 



Retina (Lat. retineo, to retain), that part of the eye which retains or receives 

 the image conveyed by the dio'ptic part. In the compound eye, the retina of 

 each ommatidium is termed a retinula. 



Saccus (Lat. =a sack or -bag), a bag-like organ. 



Sarcolemma (Gr. o-o'p|, flesh, muscle ; AeV/xa, husk, peel), the elastic sheath 

 enclosing a muscle-fibre. 



Sclerite (Gr. a~K\r)p6s, hard), a separate hardened piece of the exoskeleton. 



Sections, thin slices through an animal or organ; usually either trans- 

 verse (in a plane at right angles to the axis of symmetry), horizontal (parallel 

 to the ventral or dorsal surface), or sagittal (in a vertical plane parallel to 

 the axis of symmetry). Most of the sections figured in this book are 10/x in 

 thickness. T.S. = transverse section, L.s. = longitudinal section. 



Sensilla (Lat., dim. of sensus, perception), a minute sense-organ. 



Seta, a bristle or stiff hair. 



Sphincter (Gr. o-^ty/crijp, a tight band), a circular band of muscle for closing 

 or constricting the lumen or orifice of a tube. 



Spiracle (Lat. spiraculum, air-hole) or Stigma (Gr. =spot), a breathing- 

 aperture; one of the openings of the tracheal system. 



Squame (Lat. =a scale), a flat piece attached to an organ. 



Sterna or Sternites (Gr. crrtpvov, breast), ventral sclerites or parts of the 

 exoskeleton. 



Stomodaeum (Gr. oro/ia, mouth; 686s, entrance), an anterior invagination 

 of the ectoderm, giving rise to the mouth and fore-gut. 



Suture (La't. sutura, a seam), the soft connecting portion between two 

 sclerites. 



Syncytium (Gr. <rvv, together; KVTOS, a cell), a layer of cells so fused 

 together that their boundaries are obliterated and their nuclei lie in a single 

 continuous protoplasmic mass. 



Synthorax, the closely fused meso- and metathorax of the Dragonfly. 

 The same two segments not so closely fused, in other Insects, are often termed 

 the pterothorax, since they bear the wings. 



Teneral (Lat. tener, tender), the term applied to the freshly-emerged or 

 immature imago. 



Terga or Tergites (Lat. tergum, the back), dorsal sclerites or parts of the 

 exoskeleton. 



Trachea (Gr. rpa^em, windpipe), an air-tube. 



