REVISION OF STREPSIPTERA PIERCE. 61 



the third segment. From the thoracic ganglion nerves pass to the 

 three thoracic segments and first abdominal. The second, third, and 

 fourth abdominal are reached by nerves from the sides of the ventral 

 ganglion and the remaining segments by nerves passing back from 

 the apex of this ganglion (Nassonow, 1892 e, pi. 2, fig. 16) (fig. 2, no. 15, 

 p. 60). 



In the adult male the central nervous system has been worked out 

 for two species. In Xenos vesparum Rossi (Nassonow) the brain 

 seems to be composed of four prominent lobes or divisions. The lat- 

 eral or optic lobes are constricted at base and almost spherical; the 

 inner or antennal lobes are also constricted in front, and point 

 diagonally outward. From behind the antennal lobes arise the cir- 

 cumcesophageal commissures, which pass down and back to the tho- 

 racic mass, which is formed by the fusion of the three thoracic and 

 first two abdominal pairs of ganglia. From this mass pass out nerves 

 to the three thoracic segments and to the first three abdominal seg- 

 ments. From the abdominal commissure pass off nerves to the fol- 

 lowing four segments. The ventral mass is composed of seven dis- 

 tinct pair of ganglia, and from it pass off nerves to the last three 

 abdominal segments (Nassonow, 1892 c, pi. 2, fig. 16) (fig. 2, no. 16, p. 60). 



In the male of Stylops melittse Brandt, not Kirby, the brain consists 

 of a very transverse mass, one-third of which on each side is the ocular 

 lobe in the form of a cylinder slightly enlarged toward its apex. The 

 two central or antennal lobes are more globose, but not prominent. 

 From these pass the antennal nerves in front and the circumoesopha- 

 geal commissures behind. The thoracic mass is composed of five pair 

 of ganglia, from which pass large nerves to the legs. This mass is 

 located in the last two thoracic segments. From the back of the 

 -thoracic mass four pair of independent nerves pass to the first four 

 abdominal segments. The ventral mass is located in the fourth and 

 fifth segments and, according to Brandt, is composed of only two 

 distinct pair of ganglia. From this mass the remaining segments are 

 supplied (Brandt, 1878) (fig. 2, no. 14, p. 60). 



In the female of Xenos vesparum (Nassonow) the nervous system 

 does not traverse as much of the body as in the male. The cephalic 

 ganglion is narrow and transverse and apparently of six lobes tapering 

 toward the ocular lobes, which reach only halfway to the sides of the 

 head. The thoracic ganglion lies in the posterior half of the cephalo- 

 thorax and gives off two pairs of nerves to the thorax and one pair to 

 the abdomen. One pair of nerves arises at the apex of this ganglion 

 and three other pair arise from the ventral commissure. The ventral 

 mass, consisting of at least six pair of ganglia lies in the third and 

 fourth segments and from it pass off nerves to the remaining segments 

 (Nassonow, 1892 c, pi. 1, figs. 9, 10, 14; Nassonow, 1897) (fig. 2, no. 

 17, p. 60). 



