56 SMITHSONIAN MISCF.LLANEOUS COLLECTIONS VOL. 85 



In the larvae of the higher Diptera the dorsal and ventral muscu- 

 lature appears to be merged into a double series of oblique muscles 

 regularly crossing one another to form a network pattern repeated 

 throughout the thorax and the abdomen (fig. 23). The only muscles 

 that preserve a longitudinal direction are two bands of ventral fibers 

 continued from the prothorax to the end of the abdomen (vi). 

 There can be little doubt that this type of musculature represents a 

 highly specialized condition, correlated with the great specialization 

 which the maggot shows in nearly all other parts of its body organ- 

 ization. The lateral muscles, on the other hand, appear to retain 

 a primitive condition. The internal laterals consist of slender fibers 

 lying on the intersegmental folds (//") along the sides of the body. 

 The external laterals (/<?) comprise a small group of fibers m the 

 side of each segment against the body wall external to the network 

 of oblique muscles. 



THE ABDOMINAL MUSCULATURE OF APTERYGOTA 



The body musculature of apterygote hexapods is not well known 

 in all the major apterygote groups ; it has been carefully studied in 

 representatives of Protura, Collembola, and Dicellura, but only casu- 

 ally examined in Thysanura. Particularly desirable, therefore, wovild 

 be a complete account of the body muscles of Machilidae and Le- 

 pismatidae. 



Protura. — The abdominal musculature of the Protura is fully 

 described by Berlese (1910) in his monograph on the " Myriento- 

 mata." In this group of hexapods, Berlese says, " the musculature 

 is extraordinarily complex by reason of the great multiplicity of 

 fibers extending in all directions, very much as in the larvae of meta- 

 bolic insects." The muscle pattern of the proturan abdomen as shown 

 by Berlese, however, is not complex by comparison with that of a 

 caterpillar or of a muscoid maggot, and the proturan body muscles 

 clearly fall into the three usual categories of insect muscles, namely, 

 dorsal muscles, ventral muscles, and lateral muscles, to which are to 

 be added the body muscles of the appendages. 



The dorsal abdominal muscles of Protura are divided into external 

 dorsals and internal dorsals. The internal dorsals (muscles of the 

 second stratum of Berlese) consist of broad bands of fibers in the 

 Acerentomidae attached on the successive tergal antecostae. In the 

 Eosentomidae they are dififerentiated into median and lateral groups 

 of fibers. The external dorsals (muscles of the third stratum of 

 Berlese) include two large ()l)]i((ue muscles on each side of each seg- 



