256 



Arthropoda. 



belong to the gemis Trichodectes, each of our common domestic animals possess- 

 ing its own species (T. canis on the dog) ; on Birds, there is a number of species 

 of other genera (no fewer than six are known, for 

 instance, from the Domestic Fowl). 



Appendix to the Oethoptera. 



The Thysanura are allied to the Orthoptera ; they 

 are apterous forms, most of which are ametabolous, and 

 possess rudimentary abdominal limbs; the 

 mouth-parts are like those of the Orthoptera. The 

 Thysamu-a may be the most ancestral of all living 

 Insects, the absence of wings is probably primitive, 

 whilst in other forms it is acquh'ed (thi'ough parasitism, 

 etc.). Of the foi-ms belonging here may be mentioned : 

 Machilis, with compotmd lateral eyes, three ocelli, and 

 eight pairs of mdimentary abdominal appendages ; and 

 the sugar- mite (Lepisma saccharina, Pig. 213), 

 which, instead of the compound eye, possesses a group 

 of ocelli on each side, and has only two pairs of ab- 

 dominal limbs ; the latter is covered with bright silvery 

 scales (flattened hairs), and is very active ; common in 

 houses. ' 



Allied to the Thysanura are the Gollemhola, genus 

 Podura, etc., also apterous and characterised by a 

 forked process arising from the tip of the abdomen on 

 the ventral surface by means of which springing move- 

 ments are accomplished; they are small, and are 

 frequently found among fallen leaves, or in similar 

 places. 



Fig. 214. Abdomen 

 ■ of Machilis seen from 

 below. / first, /' last 

 -abdominal appendage, op 

 ovipositor, r, r^ eerci 

 (out away). — After Oude- 

 maus. 



Order 2. Rhynchota or Hemiptera. 



The Rliynchota, like the Insects of the previous order^ are hemi- 

 metabolous. The mouth-parts are modified to form a suctorial 

 apparatus, the proboscis, the structure of which has been 

 already described (p. 234). In some, the proboscis projects in front, 

 in others it is turned ba,ck under the body. 



Sub-Order 1. Homoptera. 



The fore and hind wings are usually alike, and both membranous* ; 

 the fore wings larger than the hind. The head is large. The proboscis 

 arises from its ventral side posteriorly, close to the thorax. All suck 

 the juices of plants. 



1. The Cicadas (Cicada), are large, rather bulky forms; the male makes 

 a peculiar noise by means of the metathoracic stigmata, which are provided with 

 vocal cords ; the tone is intensified by complicated resonators. The female 



' Not infrequently the fore wings are leathery over their whole extent. 



