212 NORTH AMERICAN SCELIPHRON (hYMENOPTERA) 



which has become closely connected with the thorax, and it was 

 regarded by early writers as part of the metathorax. Behind 

 the propodeiim is a very slender cylindrical petiole, which sud- 

 denly enlarges near its posterior end to the size of the abdomen. 

 The petiole and its enlarged posterior portion form the second 

 abdominal segment proper, but for our purpose it can be regarded 

 as the first segment of the abdomen. 



The propodeum, therefore, lies between the metathorax and 

 the petiole and is fused with the former, except for a dorsal fissure 

 separating it from the postscutellum. 



Its dorsal surface or dorsum extends from behind the post- 

 scutellinn to the point where the body begins to slope ventralh' 

 towards the base of the petiole. This point is marked by a more 

 or less distinct fovea or pit. The shape of the dorsum varies 

 with the species, since its posterior margin may be evenly rounded, 

 or its sides may converge to a point. Its surface may be more or 

 less striated, and a median groove may be present or absent. On 

 each side of the dorsum is a spiracle belonging to the propodeum; 

 this lies in the anterior half of the segment in the line of the 

 depression which marks the limits of the dorsum. The portion 

 of the propodeum behind the dorsum is termed the end by Fer- 

 nald. It extends posteriorly as far as the petiole and its hinder 

 margin is strongly reflexed to prevent too great dorsal flexure of 

 the petiole. The end is bounded laterally by a faint depression 

 extending forward on each side from the l^ase of the metacoxa 

 to the stigma or spiracle. This is known as the stigmatal groove. 

 Between this groove and the metapleuron is the remaining por- 

 tion of the median segment, known as the side. 



The somewhat slender petiole is usually narrower basally than 

 clistally. It varies in length usually with the size of the specimen, 

 and has a slight downward curve. At the base of the dorsal side 

 of the petiole is a small elevator muscle called the funiculus. As 

 mentioned above, the petiole is a slender cylinder for the greater 

 part of its length, but enlarges dorsally near its hinder end to 

 join the second segment of the abdomen. The sternal portion of 

 the cylinder extends continuously to the sternum of the second 

 abdominal segment, with which it is connected l\v a membranous 

 strip. The dorsal poilion of the cylinder is shorter, thus giving 



