Proceedings of the United States National Museum . t skin. In most endoparasites the mandible iswithout teeth. The labral sclerite is present in most ectoparasitesand absent in most endoparasites. The epistoma and the labralsclerite are rarely present together, except in the Tryphoninae, wherethe epistoma is slender. It is difficult to suggest a reason for anterior retractor muscles of the labrum insert on the medianpart of the labral sclerite (Short, 1952, p. 39, fig. 7b). It is notlikely that the labral sclerite could brace the cranium in any way asa substitute for the epistoma. The
Proceedings of the United States National Museum . t skin. In most endoparasites the mandible iswithout teeth. The labral sclerite is present in most ectoparasitesand absent in most endoparasites. The epistoma and the labralsclerite are rarely present together, except in the Tryphoninae, wherethe epistoma is slender. It is difficult to suggest a reason for anterior retractor muscles of the labrum insert on the medianpart of the labral sclerite (Short, 1952, p. 39, fig. 7b). It is notlikely that the labral sclerite could brace the cranium in any way asa substitute for the epistoma. The epistoma is well developed inlarvae with powerful mandibles. The closing apparatus of the spiracle adjoins the atrium in mostendoparasites, whereas in ectoparasites it may adjoin the atrium or besituated some distance from the atrium. There is no obvious explana-tion for this. It is generally assumed that the spiracles are open inendoparasites in the final instar larva, which is carnivorous, feeding on ICHNEUMONID FINAL INSTAR LARVAE—SHORT 505. f\—\-<ij-r\—rv^ A—? r\ ^ /\ r\ Olmm Figure 64.—Cryptinae:Hemitelini, head sclerites: Atractodes sp. (1, antenna; 2, spiracle; 3, skin.) the tissues of the host and hberating air from the tracheae. If thespiracle is open there is possibly some biological advantage in havingthe closing apparatus situated close to the atrium. If one function ofthe closing apparatus is to prevent the entry of body fluids of the hostinto the tracheal system, then it is best situated to perform this func-tion when it adjoins the atrium. If, however, such a precaution werenecessary, one would more readily expect to find hydrofuge structuresat the opening of the tracheal system, as in many aquatic insects. The setae of the sldn of endoparasites are reduced. It should be noted that the Cryptinae, which contain both ecto-parasites and endoparasites of prepupae and pupae, show larvalcharacters which are relatively uniform within the group. Just as som
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