2(S<S Annals Entomological Society of America [Vol. XI, 



are discussed under the latter region. In the pharynx the 

 epithelium is simple and is not thrown into the folds so charac- 

 teristic of the oesophagus, and this character helps to distinguish 

 between the two regions. 



THE (ESOPHAGUS. 



Intima. In this region the intima, which is comparatively 

 well developed, appears, in cross sections, to be thrown into a 

 series of strong longitudinal folds, usually six in number. The 

 primary intima is well developed; the secondary intima is 

 thicker, and stains with eosin. The primary intima bears 

 sharp backward directed spines. The apparent teeth which the 

 folds make almost close the lumen at the anterior end. but 

 become weaker and weaker posteriorly. 



Epithelium. The epithelium of the oesophagus is composed 

 of large cuboidal cells; the cell divisions are not always clear, 

 but this is doubtless due to the fixative, and does not represent 

 any tendency toward a syncytium. There is a great variation 

 in the size of the cells. The cytoplasm, which stains a violet- 

 pink with eosin, appears almost homogeneous; it is non- 

 granular and non-vacuolar. The nuclei are round-oval both in 

 cross and longitudinal sections; they are comparatively small, 

 and are densely filled with coarse deep-staining chromatin 

 granules. 



There is no indication of salivary cells in the oesophagus as 

 were reported for Hydrophilus by Plateau (1874), and have 

 since been recorded for several other insects. 



Just after a molt, and throughout each instar, the epithelial 

 cells lie close against the intima, and the above description has 

 reference to such a condition. But several days before the 

 insect is ready to cast its skin, a very characteristic premolting 

 condition develops. The cells, which seem to be glandular in 

 their nature, appear to secrete a fluid beneath the intima. 

 They become fibrillar entad, and the spaces between the narrow 

 cytoplasmic strands are probably filled with a secretion. As 

 this process continues, in a characteristic section, the epithelium 

 seems separated from the intima by a fibrillar vacuolar portion, 

 which stains light blue with Delafield's haematoxylin. Toward 

 the end of each instar the fibrillar portion constitutes the bulk of 

 the apparent teeth which the folds of the intima make, and the 



