8 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 121 



axis of the body. Cook (1949) states that the mandibular-maxillary 

 complex is used for sweeping food into the oral cavity rather than for 

 chewing. 



The 2-segmented antennae are located near the apex of the ocular 

 lobes but the exact position varies with the species as does the size 

 and shape. 



On the ventral surface of the head (fig. 4) there is a membranous 

 area that outlines the labium. The large posterior part of the labium 

 is the submentum. Directly anterior to the submentum is the pre- 

 mentum and the palatum. The latter structure, as pointed out by 

 Cook, is apparently an adaptation for rooting up material. Cook also 

 reported that labial palpi and a hypopharynx are lacking in stratio- 

 myid larvae. The arrangement of the previously mentioned struc- 

 tures is shoA\Ti in figure 5. The most important feature illustrated 

 here is the arrangement of 2 sclerotized plates that are located beneath 

 the pharynx at the posterior end of the head capsule. These struc- 

 tures function as a mortar and pestle, grinding up the food material 

 that is swept into the mouth by the manibular-maxillary complex 

 (Bischoff, 1925; Cook, 1949). The bowl-like mortar is very heavily 

 sclerotized and convoluted while the pestle, which is formed by the 

 floor of the pharynx, is modified in the form of a heavy, corrugated 

 plate and fits into the bowl of the mortar. 



If the mortar and pestle do indeed perform the task of grinding the 

 food, it seems inconceivable that stratiomyid larvae could be pre- 

 daceous on other larvae as has been reported, especially when the size 

 of the oral cavity is taken into consideration. 



Thorax. — The thorax is composed of the first 3 body segments 

 posterior to the head. The noteworthy characteristics foimd here are 

 the prothoracic spiracles, which vary in size and shape, the chaetotaxy, 

 and the shape of the segments, which seem to become broader toward 

 the metathoracic segment. Stratiomyid larvae are \\ithout legs or 

 prolegs. 



Abdomen. — This tagma consists of the 8 body segments posterior 

 to the metathoracic segment. They are similar in form to the thoracic 

 segments but differ in chaetotaxy and in occurrence of special organs 

 or structures. Several genera can be distinguished by the markings 

 or color patterns that occur on the thoracic and abdominal segments. 



The first and second segments are usually the broadest. The re- 

 mainder of the segments either taper toward the apical segment 

 (aquatic species) or several segments are parallel sided and the re- 

 mainder taper toward the apical segment (terrestrial species). At the 

 extreme end of the apical segment, which is often much longer than 

 it is wide (fig. 107), especially in the aquatic species, there is located 

 a transverse fissure that houses the spiracular chamber. In the genus 



