1911] Muir and Kershaw — Embryology of Head of Pristhesancus 79 



to the claustrum salivse (Hansen) of Diptera, and is a development 

 of the salivary ducts. This can be plainly seen in the embryo 

 about the fifteenth day, when the syringe is in the shape of a 

 sack-like dilation of the common salivary duct, stiffened with 

 spiral threads, eventually becoming chitinous, and tnd whe ehere 

 the muscle is attached invaginated (Fig. 17). Our studies gave 

 us no clue to the missing palpi. 



EXPLANATION OF PLATES 9 AND 10. 



Fig. 1. 

 Embryo of fifth day. 



Fig. 2. 

 Embryo of sixth day. 



Fig. 3. 

 Embryo of seventh day; a = embryo, b= Right mandible and maxilla. 



Fig. 4. 

 Embryo of eighth day; a = embryo, b = Left mandible and maxilla. 



Fig. 5. 

 Head of embryo of ninth day; a = head, b = Right mandible and maxilla. 



Fig. 6. 

 Embryo of tenth day; a = embryo, b = Left mandible and maxilla. 



Fig. 7. 

 Head of embryo of eleventh day. 



Fig. 8. 

 Head of embryo of thirteenth day. 



Fig. 9. 

 Head of embryo of fourteenth day. 



Fig. 10. 

 Head of embryo of sixteenth day. 



Fig. 11. 

 Head of embryo of eighteenth day. 



Fig. 12. 

 Head of embryo of twentieth day. 



Fig. 13. 

 Head of embryo of twenty-first day, 9 a. m. 



Fig. 14. 

 Head of embryo of twenty-first day, 12 noon. 



Fig. 15. 

 Head of nymph of twenty-first day, when nymph is half-way out of egg. 



Fig.*16. 

 Head of nymph when just hatched out. a = dorsal view, b = side view, c = front 

 view. 



Fig. 17. 

 Salivary syringe of embryo about fifteenth day. 



