62 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



II. Ventral muscles. — A group of internal transverse interseg- 

 mental sterno-pleural fibers (A, 7) ; an oblique intersegmental sterno- 

 sternal muscle (A, 8) ; two inner longitudinal intersegmental ven- 

 trals (A, Q, 10) ; five outer oblique intersegmental ventrals, four 

 of w^hich are median (B, //, 12, jj, 14), and one lateral {15). 



III. Lateral muscles. — An anterior intraseg mental tergo-pleural 

 muscle (A, B, 16) ; an oblique intersegmental ster no-tergal muscle 

 (A, //) ; an oblique intrasegtnental tergo-sternal muscle (A, B, 18) ; 

 a series of five intrasegmental transverse tergo-sternal muscles (A, 

 ip, 20, 21 , 22, i'j) ; two short lateral intra-tergal muscles (D, 24, 

 2_j) ; two small anterior intrasegmental tergo-pleural muscles (D, 

 26, 2/) ; two median intrasegmental pleuro-sternal muscles (C, D, 

 28, 2p) ; an oblique intersegmental pleuro-sternal muscle (A, B, C, 

 jo) ; a group of small external posterior lateral intrasegmental mus- 

 cles (C, 31, 32, 33, 34, 55; D, 38) ; and two small posterior interseg- 

 mental muscles, one sterno-pleural (C, ?6), the other pleuro-sternal 



C?7)- 



IV. Muscles of the stylus. — Two small muscles (D, jp, 40) 

 arising in the posterior lateral lobe of the sternum, inserted on the base 

 of the stylus (^^3')- 



This complex and strongly developed musculature of Heterojapyx, 

 which presumably is characteristic at least of the Japygidae, contains 

 nothing to suggest that it represents the primitive plan of the body 

 .musculature of insects. It indicates, on the other hand, a highly 

 specialized condition giving to these very small creatures a strength 

 out of proportion to their size, which might enable them to burro\v 

 into hard soil or to insinuate their bodies into minute irregular spaces. 

 In the multiplicity of individual muscles and in the diversity of 

 their attachments, the body musculature of Heterojapyx resembles 

 that of a caterpillar, but there is not the remotest likeness in detail, 

 showing that the complexity of the muscle pattern in each case is but 

 the result of a high degree of specialization adaptive to demands for 

 dexterity of body movements. Both the caterpillar and Heterojapyx 

 demonstrate the limitless potentiality of the insect muscular system, 

 and make it all the more surprising that there are so few departures 

 from the fundamental plan of muscle arrangement. 



IV. THE ABDOMINAL APPENDAGES 



There is no more vexing subject in the whole field of insect mor- 

 phology than that of the homologies of the appendicular organs of 

 the abdomen. Embryology shows at most that these organs are de- 



