58 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



probably represents a special development. The Protura have no 

 transverse muscles. Berlese describes a dorsal septum above the 

 alimentary canal, but, he says, it is composed entirely of a connective 

 tissue membrane and contains no muscle fibers. A closed dorsal vessel 

 is likewise absent. 



Collembola. — The account of the body musculature of the Collem- 

 bola given by Lubbock (1873) is so complete and so convincing in 

 its detail that no doubt can be entertained of its accuracy, though 

 apparently no subsequent investigator has verified it, or given any 

 attention to the musculature, other than that of the appendages, in 

 this interesting group of insects. Lubbock describes the muscles of 

 Tomocerus as an example of the musculature of a " linear " species, 

 and those of Smynthurus to illustrate the musculature of a '" globular " 

 species. It is clear that the muscle pattern in the abdomen of the 

 former is more generalized than in that of the latter, but that in both 

 forms the musculature is modified in adaptation to the specialized 

 functions of the abdominal appendages. 



The abdominal musculature of Tomocerus is highly developed, 

 consisting of strong bands of longitudinal dorsal and ventral muscles 

 differentiated into internal and external groups of fibers, and of 

 vertical and oblique dorsoventral lateral muscles. Li the first segment 

 two strong muscles arising on the tergum are inserted on the eversible 

 vesicle of the collophore. In the third segment groups of lateral 

 muscles are attached ventrally on the sternal region in the neighbor- 

 hood of the tenaculum, but they do not appear necessarily to be 

 primarily muscles of the pair of appendages presumably combined 

 in this organ. The muscles of the furcula, or spring supported on the 

 fifth segment, take their origins in the fourth and third segments, 

 but they appear to be parts of the system of longitudinal body muscles 

 rather than specific muscles of the leaping appendage. In Smynthurus 

 the abdominal musculature is highly modified. The longitudinal mus- 

 cles appear to be reduced and are mostly absent in typical form. On 

 the other hand, there is a great development of vertical and oblique 

 dorsoventral muscles associated with the base of the furcula, taking 

 their origins in the posterior and middle parts of the abdomen. 



In no respect can the collembolan musculature be said to be primi- 

 tive ; but it is evident that it may be derived from the same generalized 

 plan of muscle arrangement that underlies the abdominal musculature 

 of adult pterygote insects. 



Dicellura. — It is most interesting to find in Grassi's description of 

 the muscles of Campodea that the pattern of the abdominal muscula- 

 ture of this primitive aptervgote insect conforms closely with the 



