92 EXPLANATION OF TERMS 



Ontogeny: the development of the individual as distinguished from that of 

 the species : see phylogeny. 



Onyches: claws of tarsi. 



Onychium -ia: small processes between the tarsal claws in many Diptera ; 

 see empodium : a more or less retractile process on the feet of some beetles : 

 in Hymenoptera, the apical tarsal joint bearing the claws: see also arolium 

 and pulvillus. 



Obolast: the primitive germinal nucleus of an egg. 



Oogenesis: the process of egg-formation. 



Oolemma: the cell wall of an egg: see vitelline membrane. 



Ootheca: the covering or case over an egg mass, as in certain Ortlwptcra : 

 see egg case. 



Opacus: opaque; a surface without any lustre. 



Opalescent: with a bluish white lustre, as in opals. 



Opalinus: =;; opalescent ; q. v. 



Opaque: without lustre: not transparent. 



Operaria: the workers in Hymenoptera. 



Operative: in working order or actually working. 



Opercula: two plates covering the vocal structure of Cicada, beneath. 



Operculum: a lid or covering: in Diptera, the cliitinous envelope covering 

 the lower part of the muscid mouth ; the labrum-epipharynx of Dimmock : 

 the scutes covering the meso-thoracic stigmata : in Alenrodidcr, the lid-like 

 structure closing the vasiform orifice ; q. v. 



Ophthalmic: relating to the eye. 



Ophthalmotheca: that part of the pupa that covers the eyes. 



Opisthogoneate: having the organs of generation at hind end of body. 



Opisthogenia: the anal angle of the secondaries. 



Opposite: placed over against, or opposed to. 



Optic: relating to the organs of vision. 



Optic ganglia: are at the sides of the procerebrum and innervate the com- 

 pound eyes. 



Optic lobes: the lateral lobes of the procerebrum in which are centered the 

 nerves supplying the organs of vision. 



Opticon: the first of a series of three ganglionic swellings in the optic nerve: 

 see epiopticon and periopticon. 



Optic segment: := procerebral segment; q. v. 



Optic tract: is the perceptive portion of the compound eye. 



Ora: a border; specifically in some Coleoptera, the lateral margin of prothorax. 



Ora coleopterorum: the margin of the elytra. 



Orad: toward the mouth. 



Oral: pertaining to the mouth. 



Oral cavity: the mouth; ^buccal cavity. 



Oral fossa: in Mallophaga, a furrow lying in front of the mandibles. 



Oral segment: that ring or segment which bears the mouth. 



Orbicular: round and flat, the diameters of the plane eciual : in some moths, 

 a round or ovil macula in the median cell. 



