1 78 Dr. H. Schaum on the Composition of the Head, 



When we determine the number of abdominal segments in 

 those insects undergoing an incomplete metamorphosis*, we 

 cannot start from the simpler organization of the larva; but we 

 have here, as in the other section, a safe guide in the stigmata. 

 With the exception of the last, all the dorsal half-segments of the 

 abdomen are provided with a pair of spiracles in the soft mem- 

 brane which connects them with the ventral half-segments ; and 

 the first is usually remarkable from its large size and its position 

 on the back of the abdomen. Beginning with the arcus bearing 

 those stigmata, we count on the back of the abdomen, in both 

 sexes of Locusta, ten parts, which at first sight appear to be 

 segments ; but, on a closer examination, we are led to the con- 

 clusion that the tenth part (called lamina supraanalis by ortho- 

 pterologists) is not to be considered as a segment. The first 

 eight dorsal half-segments are easily identified by their stigmata 

 (PI. VI. fig. 1. 1-8); the ninth has no stigmata, and is differently 

 shaped in both sexes (figs. i. & n. 9), but is still united by a con- 

 nective membrane to the last ventral half-segment, while the 

 tenth (figs. i. & ii. c), provided on its under side with a pair of 

 sti/li (d), and also differently shaped in both sexes, is not con- 

 nected by a membrane to the ventral segments. The number 

 ' of the latter amounts to eight in the male, and to seven in the fe- 

 malef, the last being differently shaped in both sexes, and bearing 

 in the male another pair of styli (fig. i.e). With the last of these 

 (eighth in the male, seventh in the female), called lamina sub- 

 genitalis by orthopterologists, the ninth dorsal half-segment 

 forms the apex of the abdomen and an involucrum both for the 

 anus and the sexual organs, the dorsal arcus (9) being the bearer 

 of the anus, and the ventral arcus (8 or 7) that of the sexual 

 organs (figs. i.& n., — the position of the rectum in the abdomen 



* With regard to the movements which some Neuroptera undergoing 

 a complete metamorphosis perform as pupae, it has lately been denied by 

 some entomologists that a distinct limit could be traced between a com- 

 plete and incomplete metamorphosis when they approach the end of this 

 period : in denying this, however, they lose sight of a fundamental differ- 

 ence in the organization of the pupa, which does not even admit the pos- 

 sibility of a passage. In the true pupa, the skin shuts both the mouth 

 and anus, so that no food can be taken and no fasces be discharged; whilst 

 in the pseudo-pupa of the hemimetabolous insects the mouth and anus are 

 open, as in the larva and in the perfect insect. 



t The posterior part of the metasternum (PI. VI. fig. i. m, coloured blue), 

 expanded between the posterior coxa:, might easily be taken for the first 

 ventral segment, as it is separated from the anterior part of the metaster- 

 num by a deeply impressed line, by which the number of ventral segments 

 would be raised to nine in the male and to eight in the female. That it is, 

 however, in reality a part of the metasternum can be ascertained when we 

 compare it with the corresponding part in Pachytylus (fig. hi.) and Forp'cula 

 (fig. v.), where there can be no doubt as to its nature. 



