and on the Number of Abdominal Segments, in Insects. 179 



being indicated in fig. n. by a double series of red, that of the 

 vagina by a double series of blue points). The ninth dorsal 

 segment is thus proved to be the last of the whole body ; the 

 tenth part (c) is nothing but a plate which covers the anus, as 

 the upper lip covers the mouth, and can as little as the latter, 

 or the anal proleg of a larva, be considered as a segment. 



In Pachytylus migratorius, also, we count nine dorsal segments 

 in both sexes, eight ventral segments in the male (fig. in.), and 

 seven in the female (fig. iv.). The ninth dorsal segment is, in 

 both sexes, apparently divided by a transverse impressed line into 

 two ; nevertheless in reality it is simple (figs. in. b 9 & iv. a 9) ; 

 the lamina supraanalis (c) and the styli (d) are analogous to the 

 same parts in Locusta. In the male, the last ventral segment 

 has also on each side a transverse impressed line (fig. in. b 8), 

 which might, as in the last dorsal segment, be considered (but 

 erroneously) as indicating the demarcation of two segments ; the 

 last (seventh) ventral segment of the female (fig. iv. b) is without 

 any trace of such a line. The ninth dorsal and the last ventral 

 half-segment, forming the apex of the abdomen (figs. in. b & i v. a), 

 involve, as in Locusta, the upper (9) the anus, shut by the lamina 

 supraanalis {c), the lower (fig. in. b 8, fig. iv. a 7) the sexual organs, 

 which open in the female (fig.iv.A) between the four parts consti- 

 tuting the ovipositor (fig. iv. a o) (as in Locusta, between the four 

 laminae of the sword, fig. n. o), and which are separated in this 

 case from the anus by a transverse septum (fig. iv. a d, where the 

 position of the rectum is, as in Locusta, indicated by a double 

 series of red, and the position of the vagina by a double series 

 of blue points*). 



* M. Lacaze Duthiers states, in his memoir on the female genital appa- 

 ratus of insects (Ann. des Sc. Nat. 1833, vol. xix.), that in Neuroptera, 

 Orthoptera, and Hemiptera, three segments (somites) intervene between 

 the vulva, which is said to open between the eighth and ninth abdominal 

 segments and the anus, said to be situated on the eleventh segment. I 

 have not been able to confirm these statements. In Hemiptera, in accord- 

 ance with the observations of Fieber (the best monographer of this order), 

 I never find more than eight dorsal segments. In the Neuroptera with 

 complete metamorphosis, there cannot be more than nine segments, as the 

 larvse have but nine. In Orthoptera, where the anus and vulva open be- 

 tween the last dorsal and last ventral arcus, forming an involucrum (the 

 ninth dorsal and the seventh ventral where that number is greatest), I see 

 nowhere even the possibility of counting eleven segments, except in 

 Acridia (Pachytylus), if there the ninth dorsal segment be counted as 

 double and the lamina supraanalis as a segment, while the transverse 

 septum (PI. VI. fig. iv. d) is considered as a ventral half-segment. As to the 

 view of M. Lacaze Duthiers, that the various female genital organs, such as 

 stiug, borer, ovipositor, &c. (the analogous composition of which in Hyrnen- 

 optera had already been proved by Prof.Westwood), are the result of modi- 

 fications of the ninth abdominal segment, I doubt much whether observa- 

 tions on the changes of that segment during the pupa state will confirm this 



