232 Annals Entomological Society of America [Vol. XIII, 



selves plainly. This layer of connective tissue elements may 

 be traced entirely around a transverse section. 



Adjoining the basement membrane are found two or three 

 layers of muscles — an inner longitudinal and an outer circular 

 layer. The longitudinal layer is not well developed, but 

 consists of scattered bundles of fibres which fit into irregularities 

 at the bases of the epithelial folds. Each muscle is composed 

 of from one to a dozen fibres. The poor development of this 

 layer would suggest that it has little if any functional impor- 

 tance. The circular layer is better developed. It consists 

 of several strata of striated muscle fibres which interweave, 

 making a network (the individual fibres do not branch), which 

 surrounds the tube. Muscle nuclei are not prominent in the 

 layers, but the fibres are easily seen and studied. 



In many parts of transverse sections other groups of 

 longitudinal muscle fibres are found outside the circular layer 

 above described. These are numerous and well developed in 

 contrast to the longitudinal layer lying at the base of the 

 epithelium. Inasmuch as the esophagus lies between the large 

 thoracic muscles which attach to the appendages, it is likely 

 that the last described elements are members of this thoracic 

 muscle mass. 



The succession of layers above described corresponds rather 

 closely to that in the esophagus of other insects. There is, 

 therefore, nothing remarkable about this organ in a structural 

 sense. 



The lumen of the esophagus is continuous with that of the 

 anterior crop through a narrow passageway running between 

 well-developed epithelial folds. These folds have at their bases 

 circular muscles and much connective tissue. A longitudinal 

 section of this region shows that this arrangement is a real 

 valve with a sphincter. It must, therefore, function in pre- 

 venting the flow of juices back into the esophagus once they 

 have arrived in the anterior crop cavity. On the esophagus 

 side of the valve the epithelium is not folded but gives a funnel 

 shape to the lumen as it runs posteriorly. On the crop side, 

 however, the epithelial lining is thrown into numerous folds 

 (Fig. 10), especially at the point nearest the actual opening in 

 the valvular structure. Liquid going in the wrong direction 

 would thus be hindered in its progress by the folds and a con- 



