DEVELOPMENT OE PHRYGANIDS. 601 



Fig. 13.— Cross section of the ventral plate in a later stage. Beneath the 

 median furrow is a group of cells uniting the lateral cords. 



Fig. 14.— Cross section of the abdomen during the stage represented in 

 PI. XXXVIa, fig. 12, showing a section of the proctodasum and the Mal- 

 pighian vessels. 



Figs. 15, 16, 19 are successive sections of the head in a plane perpen- 

 dicular to the front wall of the cranium. Fig. 16^? shows a pair of ectodermic 

 rods forming a part of the endocranium. Fig. 15 is a section dorsal to the 

 one just described ; c, the so-called egg-rupturing organ, whose function, 

 however, is still very doubtful, and which may represent the simple eye of 

 Insects ; b, a structure, probably of a ganglionic nature, connected with the 

 simple eye ; ectodermic ingrowths are developed on either side of these 

 organs. Fig. 19, a section dorsal to that in Fig. 15, showing at a the ecto- 

 dermic thickenings to form the eye ; en. c, a group of vesicular endoderm 

 cells on the ventral side of the oesophagus. 



Fig. 17. — Cross section of the blind end of the proctodaeum, showing the 

 three separate pairs of invaginations to form the Malpighian vessels. 



Fig. 18. — Cross section of the folded abdomen in the region marked an.st., 

 PI. XXXVIa, fig. 12. a is the median infolded portion of the ectoderm 

 uniting the lateral cords ; a. st., anal stylets. 



Fig. 20. — Cross section of first abdominal segment, en. c, yolk-cells mi- 

 grating into the body cavity; to. ot., somatic mesoderm; 5/7. »/., splanchnic 

 mesoderm. The arrows indicate the directions in which the mesodermic folds 

 are growing. 



PLATE XXXV Ic. 



Fig. 21. — Cross section through the first maxillae and procephalic lobes. 

 In the deep surface of the lateral cords dark granular cells appear, which 

 finally replace the more lightly stained ones. The stage corresponds to that 

 shown in PI. XXXVIa, fig. 10. 



Fig. 22. — Longitudinal section of embryo corresponding to PI. XXXVIa, 

 fig. 12. 



Fig. 23. — Cross section through the mandibular segment of an embryo 

 corresponding to PI. XXXVIa, fig. 12. 



Fig. 24. — Cross section through abdomen of larva, a, segmentally ar- 

 ranged thickenings of the liypodermis ; y, one of the wandering endoderm 

 cells. 



Fig. 25. — Cross section of salivary gland of larva. 



Fig. 26. — Longitudinal section of a part of the same gland. 



Fig. 27. — Muscle cells of the larva. 



Fig. 29. — Section of one of the large cavities in the body of the larva. 

 d, amoeboid endoderm cells attached to its wall. 



