NO. 6 INSFXT ABDOMEN — SNODC.RASS 57 



ment ; one (the intersegmental tergal muscle of Berlese) arising 

 medially on the anterior part of the tergum and inserted laterally on 

 the antecosta of the following tergum, the other (the intersegmental 

 tergopleural muscle of Berlese) arising anteriorly on the tergal ante- 

 costa and inserted posteriorly on the " pleuron " of the following 

 segment. The so-called " pleuron," however, is probably to be re- 

 garded as a paratergal sclerite. 



The ventral muscles of the abdomen include likewise external 

 ventrals and internal ventrals. The internal ventrals consist of paired 

 bands of longitudinal fibers extending throughout the length of the 

 abdomen. Each muscle band is divided into a median group of fibers 

 attached on the sternal antecosta of each segment, and into longer 

 lateral muscles in the first five segments attached on alternate sterna. 

 The external ventrals occur only in the first three abdominal seg- 

 ments of Acerentomidae. Those of the first segment extend from the 

 center of the sternum laterally to the bases of the appendages of 

 this segment, and serve as adductors of the appendages. In the sec- 

 ond and third segments corresponding pairs of muscles arising on 

 the anterior median part of each sternum diverge posteriorly to the 

 antecosta of the following sternum. 



The lateral musculature of the alxlonien in Protura has a very sim- 

 ple pattern. The lateral muscles comprise intrasegmental vertical 

 tergo-sternal muscles, and intersegmental oblique tergo-sternal mus- 

 cles. The intrasegmental laterals include in each of the first three 

 abdominal segments of Eosentomidae, and in the first segment only of 

 Acerentomidae, a pair of tergal muscles inserted ventrally on the base 

 of the appendage, and in the following segments of Acerentomidae 

 a single lateral tergo-sternal muscle. The intersegmental laterals con- 

 sist of two slender muscles arising laterally at each end of the tergal 

 antecosta in each segment, one of which goes to the anterior margin 

 of the sternum of the preceding segment, the other to a corresponding 

 point on the sternum of the following segment. From the first ab- 

 dominal tergum a muscle extends downward to the posterior edge of 

 the metathoracic sternum, and another goes forward to the posterior 

 edge of the mesothoracic sternum. 



An analysis of the proturan musculature, as described by Berlese, 

 thus shows that the Protura suggest nothing different as to the pattern 

 of the primitive body musculature of the Hexapoda from the idea 

 to be derived from a study of the muscles of adult Pterygota. 

 Since the lateral musculature in the Protura does not match with that 

 of any pterygote insect, it does not appear to be the prototype of 

 the lateral musculature characteristic of the Pterygota, and therefore. 



