598 ROBERT MATHESON 



in the oesophageal valve region where the cells become elongated 

 and narrowed and the cell walls more distinct. The nuclei are 

 more crowded and more chromatic. The cytoplasm appears 

 more granular and shows a sharper differential staining reaction. 

 The intima shows little change except for a slight granular appear- 

 ance near the epithelial cells. It has not yet become separated 

 from the epithelium. These general observations hold for the 

 entire fore-gut at an early prepupal stage. But in the anterior 

 portion the cells do not elongate so much nor do the cell walls 

 become so sharply differentiated. There is no imaginal ring 

 present and the pecidiar glandular cells found between thefore- 

 and mid-guts show no activity throughout the entire prepupal and 

 pupal periods. 



The absence of an imaginal ring is in marked contrast to the 

 condition described by several authors for a number of other 

 insects. In all the dipterous forms so far carefully studied an 

 imaginal ring is recorded (Ganin '76, Kowalevsky '87, Van Rees 

 '89, Vaney '02 and Perez '10). It is recorded as present in the 

 Hymenoptera by Ganin ('76) for Formica and Myrmica, and 

 Perez ('02) for Formica. Karawaiew ('98) notes its absence in 

 Lasius fllavus, Anglas ('00) in the bee and wasp, and Van Leeuwen 

 ('07) in Isosoma graminicola. In the Coleoptera Ganin (76) 

 finds it in Chrysomela and Tenebrio, Deegener ('00) and ('04) 

 in Hydrophilus and Cybister. Karawaiew ('99) notes its absence 

 in Anobium paniceum. Ganin ('76), Verson ('98) and Deegener 

 ('08) record its presence in Lepidoptera (Lithocolletis, Bombj-Tc 

 mori and Malacosoma castrensis). In the Trichoptera Lubben 

 ('67) regards the imaginal ring as absent while Russ ('08) records 

 a prominent one for Anabolia laevis. 



In a slightly older prepupa than that just described the intima 

 becomes completely separated from the epithelium. The inner 

 surfaces of the cells show in many places small, protoplasmic 

 projections as if they had been drawn out of the intima. These 

 are not shed into the lumen but later become flattened down. 

 There are no signs of degeneration. The nuclei show their char- 

 acteristic staining reactions while the cytoplasm remains granular 

 (fig. 19). The intima, however, shows considerable change. 



