224 INDEX OF SCIENTIFIC TERMS 



Ocular tubercle — prominence bearing the eyes in harvestmen and some 

 spiders, etc. 132-3, 135, 145 



Odoriferous glands — repugnatorial glands (q.v.) 



Ontogeny — origin and development of an individual living being as dis- 

 tinguished from phylogeny (q.v.) 



Operculum — exoskeletal plate forming a lid or cover. See genital oper- 

 culum 



Opisthosoma — posterior region of the body of Arachnids, often known 

 as the abdomen 



Ovoviviparous — retaining the eggs inside the body of the mother, 

 although within the egg-membrane, until the embryos are fully de- 

 veloped so that living young are produced 



Osmosis — flow^ of water from a weaker to a stronger solution through a 

 semi-permeable membrane 206 



Palp — pedipalp (q.v.). Also tactile head appendage of insects, crus- 

 taceans, myriapods, etc. 



Papilla — a projection 



Parasitoids — parasitic insects which, like Ichneumon wasps, eventually 

 kill their host 11,169 



Parthenogenesis — the development of unfertilised eggs 



Patella — short leg segment between femur and tibia 



Pectine — comb-like sense-organ on ventral surface of abdomen in scor- 

 pions 71, 76-8, PI. IXb, Xa 



Pedicle — the narrow 'waist' of an Arachnid uniting the prosoma and 

 opisthosoma 



Pedipalp — leg- like tactile organ in front of the legs of an Arachnid form- 

 ing claw of scorpions, reproductive organ of male spiders, etc. 



Penolic tanning — sclerotisation (q.v.) 



Phoresy — utilisation of another animal for transport 30, 101, 103, 

 142 



Phototaxis — directed response in relation to the stimulus of light 



Phylogeny — evolutionary change in the ancestry of a living organism. 

 Cf. Ontogeny (q.v.) 



Planidium larva — active larva of parasitic Hymenoptera developing 

 from an egg laid away from the host. It is a migratory form adapted to 

 seek out the latter 3 1 



Plantigrade — walking on the sole of the foot or on a flat termination of 

 the limb and not on the toes or claws. Cf. Digitigrade (q.v.) 46 



Pleopods — plate-like, respiratory endopodites of abdominal limbs of 

 crustaceans 2, 6 



Pleurite — chitinous plate forming the side of a body segment 



Propeltidium — front portion of carapace in Schizomida 121-2 



Proprioceptors — sense organs that detect the positions and movements 

 of different parts of their possessor's body 138 



