OF OECANTIIUS AND TELEAS. 2'/ 5 



PLATE XIX. 



Fig. 1. Dorsal view of an embryo showing the relations of the "gill-pads," /, to the body. X 50. 



Figs. 2,3. Lateral and ventral views, respectively, of the same embryo in situ. X 50. The embrjo 

 has almost completed its revolution. The abdominal flexures have disappeared so that the proctodaeum 

 now projects into the yolk and lies dorsad to the nervous cord. 



Fig. 4. An embryo in which the yolk has all passed into the mesenteron. The remains of the yolk sac 

 (serosa) are seen as a plug-like cylinder, continuous with the mesenteron but still projecting beyond the 

 region of the body wall. The stomodaeum and proctodaeum have united with the mesenteron. The Mal- 

 pighian tubes are sprouting out from the proctodaeum. The " gill-pads " hfive disappeared; the thoracic 

 appendages and the mouth parts are confined to the now much narrower ventral area. X 50. 



Fig. 5. An embryo, some time after revolution, in which the mesoderm plates have coalesced in the 

 median dorsal line. The opening into the yolk sac is much reduced. X 50. 



Fig. 6. Frontal view of the lobes of the brain, which are not yet united. From an embryo in clove 

 oil. X 50. 



Fig. 7. Frontal view of the mouth parts (labrum, first and second maxillae, — the mandibles lie 

 beneath the maxillae) after the closure of the dorsal wall. X 05. 



Fig. 8. The mouth parts of another individual near this stage, dissected out to show the lobes of the 

 first and second maxillae. X 65. 



Fig. 9. The three thoracic ganglia dissected from an embryo at this stage. Acetic-acid carmine, balsam 

 preparation. X -400. The cross commissures in the lower ganglion are filled in from another specimen 



Fig 10. Frontal view of the brain and suboesophageal ganglion in situ, showing their connection by the 

 commissural cords. From an embryo treated with osmic acid, picro-carmine, clove oil, balsam. X 125. 



Fig. 11. Optical section of the germinal band of Oecanthus in the sagittal plane, showing the relations of 

 the cells in the free state. X 560. 



Fig. 12. The corpus adiposum and pigment bodies of the right halt' of one of the abdominal segments of 

 the embryo fig. 1. X 125. 



Fig. 13. The free end of the stomodaeum after its lumen has opened into the mesenteron, to show its 

 structure. The epithelial layer is thrown into six folds, while the muscular layer surrounds this thickest 

 portion by a very thin layer of cells. X 400. 



Fig. 14. A portion of the antenna of an embryo after hatching showing the spines as cuticular out- 

 growths, one to each cell. X 125. 



Fig. 15. Dorsal aspect of the left anal stylet from the same embryo with its balloon-shaped oivan and the 

 hairs. X 65. 



Fig. 16. The balloon organ from the above, showing its peduncle. X 100. 



Fig. 17. A ventral view of the embryo at the time of revolution, the gill-pad should have been repre- 

 ented as though seen through the body. X 65. 



PLATE XX. 



Fig. 1. Oecantlms. An ovariole dissected in osmic acid, stained in picro-carmine. X 160. 

 Figs. 2 and 3. Ovarioles of Oecantlms prepared in sodium chloride, glycerine. X 160. 

 Fig. 4. A follicle of Oecantlms from a sodium chloride, picro-carmine, glycerine preparation. X 85. 

 Fig. 5. The upper end of an ovariole of Periplaneta sp. from a dissection in osmic-acetic solution hard- 

 ened in alcohol ; balsam preparation. X 400. 

 Fig. 6. An ovum from the same. X 800. 



Fig. 7-10. Four consecutive stages in the revolution of the embryo. X 15. 

 I. At the time of the fusion and rupture of the serosa and amnion. 

 II. After the head of the embryo has passed through the rupture. 



III. The body of the embryo lies curved in the bottom of the egg; the abdominal flexure still 

 persists. The amnion covers only the latter part. 



IV. The embryo has completed the revolution, and the serosa has contracted into a thick-walled sac, 

 but has n .1 changod its position. The amnion has turned inside oat and now forms the dorsal and part 

 of the lateral walls of the embryo. The proctodaeum and stomodaeum are enclosed between the dorsa 



