NO. 6 



INSECT ABDOMEN — SNODGRASS 



73 



The typical spring, or leaping organ of the Collembola, known as 

 the furcula (fig. 30 D), has quite a different type of structure from 

 that of the coUophore. It consists of a large median base, the manu- 

 brium (mn), and of two slender arms, each of which is subdivided 

 into a long proximal segment, the dens (d) , and a short terminal 

 segment, or mucro (w). On the base of the manubrium are inserted 

 flexor and extensor muscles arising in the fourth and third abdominal 

 segments, but, as already observed, these muscles apparently belong 

 to the system of longitudinal dorsal and ventral body muscles, and 

 are not specifically muscles of the spring. In Tomocerus vulgaris 



Fig. 30. — Abdominal appendages of Collembola. Tomoccrns vulgaris. 



A, lateral view of insect. B, anterior view of collophore. C, tenaculum. D, 

 furcula. 



a, aperture between bases of furcular arms receiving- prongs of tenaculum ; 

 ab, abductor muscle; ad, adductor muscle; Col, collophore; d, dens; Fiir, fur- 

 cula; m, mucro; vjh, manubrium; rv, retractor muscles of vesicle; v, terminal 

 vesicle of collophore. 



(fig. 30) each of the arms of the furcula is provided with an abductor 

 muscle (D, ah) and an adductor muscle {ad) having their origins in 

 the manubrium. According to Quiel (1915) adductor muscles are 

 absent in Orchcsella cincta, though he says a few obliquely transverse 

 fibers are present in the manubrium. It is possible that Quiel did 

 not observe in studying sections that these transverse fibers are 

 attached on each side to a slender adductor tendon of the dens. The 

 structure of the furcula readily suggests that it is composed of a 

 pair of segmental appendages united by a fusion of the coxae, which 

 become the manubrium, while the reduced telopodites become the 

 arms. 



