No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 137 



of cells, the suboesophageal body, colored pink in the figure, 

 extends between the oesophagus and the mandibular somites. 

 The origin of this mass is obscure. It may arise from the 

 ectoderm of the oesophagus, to the inner end of which it is 

 attached (Fig. 61), or it may come from the entoderm {eti). I 

 believe, however, that it arises from neither of these sources, 

 but from the mesoderm, which in a preceding stage formed 

 the abortive somites of the tritocerebral segment. In frontal 

 section (Fig. 62) the mass of cells is A-shaped, with the 

 juncture of its two arms attached to the lower surface of 

 the oesophagus. The distal ends of the arms are applied to 

 the anterior walls of the mandibular somites. The separate 

 cells are often sharply wedge-shaped and appear to be sepa- 

 rated by clear spaces. They grow somewhat, lose their triangu- 

 lar outline and become more rounded. At the same time they 

 tend to fuse in curved strings, with their broad edges applied 

 to one another. This condition is seen in Fig. 63, which is 

 taken from a section through the organ of an embryo in Stage 

 G. The cytoplasm is now very granular, and has a distinctly 

 yellow tint even in unstained sections ; like the neuroblasts 

 and germ-cells it absorbs picric acid with avidity. Vacuoles 

 have begun to make their appearance, and the walls between 

 adjacent cells are disappearing. The volume of the nuclei 

 remains constant, but the cytoplasm enlarges up to the time 

 of hatching. Fig. 64 is a part of a section through the sub- 

 oesophageal body of a 7 mm. larva of XipJiidmm fasciatiini. 

 The condition of the organ is essentially the same as at the 

 time of hatching. The increase in volume of the cytoplasm is 

 clearly shown. Instead of being granular, as in the younger 

 stages, the protoplasm is now so filled with small vacuoles that 

 it is reduced to a coarse reticulum. 



In the suboesophageal body of a larva 9 mm. long, signs 

 of degeneration have begun to appear. The small vacu- 

 oles fuse in the centres of the cells, leaving only the cell- 

 walls as ragged envelopes. The nuclei become somewhat poly- 

 gonal in outline. At this time the organ is found attached to 

 the anterior ends of the salivary glands and to the large trunks 

 which run forward into the head from the first thoracic trachere. 



