48 C. HERBERT HURST. 



apparently, of nine segments. The ninth segment bears four gill- 

 plates surrounding the anus, and on its ventral surface, the median 

 series of long setae which serves as a propeller. 



Eespiration, according to Easchke, is performed in a threefold 

 manner ; by the gills just mentioned, by the rectum, and directly, 

 the air being taken into the tracheae by a conspicuous siphon pro- 

 jecting upwards from the eighth abdominal segment. The tracheae 

 of the abdomen serve not only as organs of respiration, but also by 

 virtue of their great size as a float, keeping the larva when at rest 

 at the surface of the water, with the hinder end upward and the 

 end of the siphon touching the surface. 



The alimentary canal is practically straight. The oesophagus is 

 narrow. The stomach is wide, and extends from the anterior part 

 of the thorax to the sixth abdominal segment. Its walls are very 

 thick, and the epithelial cells very large, and in the thorax it has 

 eight diverticula or pouches. From its hinder end the small intestine 

 runs backwards to open into the wide rectum at the anterior 

 end of the eighth abdominal segment, and this leads direct to the 

 anus at the end of the body. 



Five Malpighian caeca lie in the hinder segments of the abdomen, 

 and open into the anterior end of the small intestine. 



A pair of sac-like salivary glands lie at the sides of the stomach in 

 the anterior part of the thorax, and their ducts, according to Easchke, 

 unite, and have their opening " oben am Beginn des (Esophagus." 



So far I have followed Easchke's account, except in ascribing a 

 hydrostatic function to the " colossal " tracheal system, which is 

 apparently much larger than would be necessary for respiratory 

 purposes alone. 



To Dr. Easchke's account I would add that, in addition to the 

 head appendages, there appear during the larval period not less than 

 eight other pairs of appendages beneath the larval cuticle. Of these 

 six pairs are thoracic and two abdominal. The thoracic appendages 

 are three pairs dorsal, the future pupal siphons, the wings and the 

 halteres; and three pairs ventral, the future legs. The two abdo- 

 minal pairs belong to the two last segments. Those of the eighth 

 abdominal segment lie in the larval siphon, and form the fins of the 

 pupa ; the hindmost pair form the outer gonapophyses of the adult, 

 which are accessory organs of copulation. 



