INDEX OF SCIENTIFIC TERMS 225 



Prosoma — anterior region of the body of an Arachnid, sometimes called 



the cephalothorax (q.v.) 

 Prosopon — adult or imago stage in Hydracarina 1 99 

 Protonymph — first nymphal stage following the larval instar of a mite or 



false-scorpion 105, 111, 112, 196, 200 

 Pseudo-tracheae — respiratory tubules in pleopods of woodlice 2, 6, 7 

 Pulvilli — lateral tarsal lobes forming suckers beneath the bases of the 



claws in Phrynichida, etc. 125, 127 

 Pygidium — posterior part of the body forming a distinct division 117, 



122,124,129 



Racquet organs — malleoli (q.v.) 



Ram's-horn organ — extrusible reproductive organ of some male false- 

 scorpions 108, 109-10 



Reflex — simple, automatic and involuntary response to a stimulus 



Repugnatorial gland — gland secreting distasteful or unpleasant liquid 

 whose function is to deter aggressors 



Sclerite — sclerotised or chitinous plate on the body of an arthropod 



Sclerotin — product of sclerotisation (q.v.) 



Sclerotisation — chemical process analogous to the tanning of leather by 



which a protein combines with a phenol or quinone to form sclerotin, 



a tough, resistant and somewhat impervious component of the arthro- 



podan integument 20 

 Scopula — brush of hairs or setae at the end of the tarsus 164 

 Scutum — dorsal plate in ticks and some mites formed by a fusion of 



tergites 184 

 Sensilla — arthropodan sense-organ 

 Serrula — row of chitinous teeth as on the maxillae or chelicerae 100, 



104, 107-8 

 Seta — hair, bristle or spine, often sensory, on the body of an arthropod 

 Somite — segment of the body 

 Spermathecae — female organs in which are stored the spermatozoa 



received from the male 110 

 Spermatophore — envelope or bag containing spermatozoa and secreted 



by some male arthropods 55, 83, 109-10 

 Spinneret — spinning organ at rear of body in spiders and on chelicerae of 



false-scorpions 104-5, 149, 161, 176 

 Spiracle — respiratory aperture, the orifice of a tracheal tube 16, 40, 42, 



44,137,183,205 

 Stabilimentum — narrow ribbon of silk on a spider's web which helps to 



camouflage the spider PI. XV a 

 Stadium — developmental stage 

 Stenothermic — unable to tolerate wide variations in temperature. Cf. 



Eurythermic (^.t;.) 190 



