280 AYERS OX THE DEVELOPMENT 



F\cs. 13, 14. Side and ventral views of another larva. The frontal process ends in an enlargement. 

 The mesenteron and stomodaeum are united. The wall of the blind end of the mesenteron could not be 

 distinguished in this specimen. X 1-5. 



Fig. 15. Side view of the cup-shaped organ of the larva represented in fig. 19. X 200. 



Fig. 16. Nuclei in the hypodermic syncytium of a larva. X 500. 



Fig. 17. An oblique ventral view of the mandibles and lower lip of another larva. X 150. 



Fig. 18. Lateral view of the end of the caudal appendage. X 250. 



Fig. 19. Ventral view of a larva soon after entering upon the cyclops stage, to show the cuticular 

 structures. X 125. 



Fig. 20. Lateral view of the same, to show the muscular system. X 125. 



Fig. 21. Second larva in which the nervous band and germs of the sexual cells are not fully differen- 

 tiated. The stomodaeum and mesenteron are fully formed but the proctodaeum has not yet appeared. The 

 muscular system is partially developed. X 125. 



Fig. 22. Dorsal view of the same individual, to show the dorsal muscles. X 125. 



Fig. 23. Lateral view of the mesenteron and nervous system of another larva. X 150. 



Fig. 24. Ventral view of the cuticular structures of the cephalo-thorax. X 125. 



Fig. 25. Lateral view of a larva approaching an ecdysis. X 75. 



Figs. 26, 27. Dorsal and posterior aspects of the genital cell mass of an individual in the cyclops stage 

 X 60. 



Fig. 28. Striated muscle from the band-like muscles of the abdomen. X 500. 



Fig. 29. Transverse section through the abdominal region. The abdominal appendage is seen in section, 

 lying above the body. The nervous cord shows a distinct lumen and lies imbedded in a mass of hypodermic 

 and mesodermic elements. X 150. 



Fig. 30. The germs of the sexual organs from another embryo. 



PLATE XXV. 



Figures 1-21 Teleas. Figures 22-33 Oecanthus. 



Fig. 1. Obliquely ventral view of a cyclops larva entering upon an ecdysis. The two swollen cuticular 

 sacs near the tin organs illustrate the manner in which cuticula and hypodermis separate. X 150. 



Fig. 2. The mass of nerve and sexual cells lying on the dorsal side of the mesenteron. 



Figs. 3 and 4. Side and dorsal views, respectively, of the germs of the sexual organs. In fig. 3 the con- 

 nection with the mesenteron is shown. X 125. 



Fig. 5. Side view of the abdominal region of another larva showing the germs of the sexual organs still 

 united to the nerve cord. They are also connected to the mesenteron by the usual protoplasmic filaments 

 X 75. 



Fig. 6. Surface view of the cup-shaped structure from the right side of the same. X 250. 



Fig. 7. Ventral aspect of the larva shown in fig. 1. X 150. 



Fig. 8. The cells of the mesenteron seen from above. X 500. 



Fig. 9. Lateral view of the larva with the. nervous system well developed. X 125. 



Figs. 10, 11. Sections of the larva, from osmic acid, picro-carmine, balsam preparations. Fig. 10. Trans- 

 verse section through the mandibular region of the head. The mesenteron is intimately connected with the 

 nerve cord. X 150. Fig. 11. Longitudinal section passing obliquely through the body. The germs of the 

 sexual organs, the abdominal nerve mass and the surface of the mesenteron are seen in this section. X 75. 



Figs. 12 - 17. Sections of the cyclops larva, from osmic acid, picro-carmine and balsam preparations. 

 Fig. 12. A portion of the cuticula of the abdomen showing the manner of origin of the mandibular mus- 

 cles. X 250. 



Fig. 13. Longitudinal section nearly parallel to the dorso-ventral axis of the body. The nervous cord 

 is seen ending in a thickened portion which is folded in an S-shaped manner. Lying dorsad of this and behind 

 the mesenteron are seen the germs of the sexual organs. X 75. 



Fig. 14. Transverse section through the abdominal region of a larva younger than that represented in 

 fig. 5. X 75. 



Fig. 15. Hypodermal layer of protoplasm containing nuclei. X 500. 



Fig. 16. Section of the germ of the sexual cells. X 250. 



