ARTHROPOD A. 



299 



PLATE IX. 



This plate represents points of interest in the anatomy of various 



groups of Arthropoda. 



FIG. i. Machilis polypoda* from Sir J. Lubbock, Monograph of the Collembola and Thysa- 

 nura, Ray Society, 1873, PI. LIII. and p. 236. 



THIS Insect belongs to the order J^kysanura, family Lepismidae. The 

 many jointed filaments borne by the last abdominal somite in this order 

 are three in number, except in the genus Campodea, where they are two, 

 and in Iapyx y in which they are represented by a pair of short stout un- 

 jointed forceps. In Lepisma the three filaments are equal in size ; in 

 Lepismina and Nicoletia the central filament is slightly longer, a difference 

 much exaggerated in Machilis. In the family Lepismidae the maxillary 

 palpi are long, and the body is clothed with scales. 



Machilis polypoda has only been found in Great Britain : it inhabits 

 woods and dry places, is about half an inch long, and is brown in colour, 

 with a metallic lustre. 



a. Antennae composed of many setose joints, tapering to their extremities 



and longer than the body. The terminal joints are united in groups 

 of seven. 



b. Maxillary palpi composed of six joints. The three terminal joints are 



recurved. 



c. Eyes. Simple according to Packard, large and black ; contiguous in 



this genus, but small and widely separate in Lepisma. 

 The above described parts are borne upon the head, which is distinctly 

 marked off from the thorax. The latter consists of three limb-bearing 

 somites as in all Insecta, but it is not distinctly marked off by any con- 

 striction from the abdomen which has ten somites. 



d. Anterior or pro thoracic legs. The pro thorax is large and arched. 



e. Meso-thoracic, or middle pair, and 



f. Meta-thoracic, or posterior pair, of limbs. 



These limbs in Machilis bear on their basal joints a short cylindrical 

 appendage covered with stiff hairs and closely resembling the cylindrical 

 appendages of the abdomen. The processes in question may be seen 

 projecting in front of the corresponding limbs. 



In Scolopendrella, a Myriapod (? Insect) classified by Packard with the 

 Thysanura, there is a similar appendage internal to the bases of each of its twenty- 

 two limbs. It may be noted also that Scolopendrella agrees with Campodea among 

 Thysanura, and with the Collembola in having both mandibles and maxillae sunk 

 in the head. 



