32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



sternal plates just in front of the coxal bases, but a curved, rodlike 

 apodeme extends outward and forward from the median line to 

 articulate with the front margin of the coxa. In addition to these 

 structures in Scutigerella (pi. ii, fig. 34) there is an unpaired ante- 

 rior sclerite and a pair of smaller lateral ones. In Scutigerella and 

 Hanseniella (pi. 11, fig. 35) the eversible sac is surrounded at its 

 base with a chitinous ring. This ring is broken in Symphylella pro- 

 ducing two crescentic pieces (pi. 12, fig. 36). 



THORACIC STERNA IN PROTURA 



Berlese (1910) was the first to describe the sternites in the Protura. 

 He found that each thoracic sternal region was covered by two large 

 sternal plates. The anterior one he called the sternum and the pos- 

 terior one the sternellum. On the lateral margin of the sternellum 

 near its anterior corner is an articulating condyle for the coxa. The 

 present writer has worked out the sternal region for Acerentuliis 

 barheri (pi. 12, fig. 37) . He has little to add to that found by Berlese, 

 but suggests the term basisternum for the more anterior of the two 

 sternites. 



In Eosentomon the second and third sternella have developed a 

 median apodeme which shows an anterior forking. This is doubtless 

 a structure found better developed in many insects, being particularly 

 conspicuous in Japyx. In Eosentomon rihagai, Berlese (1910) 

 represents the third sternellum with the forks of the Y passing later- 

 ally to the articulating condyles for the coxae. In Eosentomon vermi- 

 fornte, an American species, the forks of the Y are found only on 

 the third sternellum. These pass outward to the articulation condyles 

 for the coxae but do not quite meet inwardly on the median line. 



THORACIC STERNA IN THYSANURA AND COLLEMBOLA 



In the Collembola the legs are brought so close together that the 

 sternal characters cannot be made out satisfactorily. 



The sternal plates of Thysanura dififer radically from those of 

 Protura in their musculature. In this order the ventral longitudinal 

 muscles extend between the posterior parts of the thoracic sterna 

 as they do in pterygote insects. This condition is radically dififerent 

 from that found in the abdominal sterna and the terga of probably 

 all insects where the longitudinal muscles attach to the anterior ridges. 

 Carpenter (1916) has figured the sternites of Lepidocampa. In the 

 case of the meso-, and the metasternum, each is provided with a 

 single plate, which has a posterior chitinized ridge and an incomplete 

 median apodeme. 



