No. 1774. THORAX OF HYMENOPTERA—SNODGRASS. 57 



with the metapostnotum of some other orders, such as the Coleop- 

 tera, which he also refers to the abdomen. In the Coleoptera the 

 postnotum of the metatergum is a very distinct plate. Wliile it is 

 sometimes attached to the front of the abdomen, it seldom appears 

 in this order to be a part of the abdominal tergum, and it nearly 

 always retains a connection with the epimera of the metathorax. 



With regard to the so-called "postscutellum" of the metathorax 

 in the Orthoptera, then, the writer reiterates his former statement, 

 that it is, by anatomical continuity, a part of the first abdominal 

 tergum. Theoretically, it may be the postnotum of the metathorax, 

 but reason should be shown why the dorsal muscles of the metathorax 

 and even the posterior phragma may not, in some cases, be attached 

 to the first abdominal tergum, just as these muscles of the meso- 

 thorax (fig. 12, DMcl) and the middle phragma {2Ph) are, in many 

 cases, attached to the front of the metathoracic tergum (N^). The 

 Mantidoj and Phasmidge do not show any anterior subdivision of the 

 first abdominal tergum, nor do they have any trace of an independ- 

 ent postnotum in either segment. Hence, the Orthoptera do not 

 have a postnotum at all in the mesothorax and, if they have this 

 plate in the metathorax, it is developed best in the higher families and 

 always apparently as an intimate part of the first abdominal tergum. 



This brings us to the question concerning the nature of the phrag- 

 mas and the reason for their relation to the postnotal plates stated 

 on page 45. The phragmas, as already described, are the internal 

 transverse plates descending into the body cavity from between the 

 thoracic and first abdominal terga. There are consequently never 

 more than three of them present; often only one or two are well 

 developed, while in some cases there are no traces of any phragmas 

 at all. Kirby and Spence (1826) named them the ''prophragma," 

 the "mesophragma," and the ''metaphragma," but, since their 

 connections with individual segments are secondary and variable, 

 it seems best to call them the anterior, middle, and 'posterior phragmas. 

 Each is composed, in its upper part at least, of two closely appressed 

 or fused laminae, and, in the adult stage, is attached to one of the 

 two adjoining terga or to both. The first or anterior phragma is 

 always, so far as the writer has observed, attached to the front of the 

 mesotergum. The second or middle phragma is sometimes attached 

 to the posterior edge of the mesotergum and sometimes to the ante- 

 rior edge of the metatergum, or, when these two plates are anchylosed, 

 to both of them. The third is always, unless the Orthoptera con- 

 stitute an exception, attached to the posterior edge of the meta- 

 tergum, or to both this plate and the first abdominal tergum when 

 these two parts are anchylosed. 



That this association of the phragmas in the adult stage with one 

 or the other of the adjoining terga is a secondary condition is sug- 

 gested by a study of figures 14, 15, and 16. The section through 



