OF OECANTHUS AND TELEAS. 277 



Figs. 5, 11 and 12. Sections of yolk nuclei from osmic-acetic acid preparations, stained in picro-carrnine, 

 mounted in benzole-balsam. X 800-. 



Fig. 8. A nucleus from the cells of the follicular epithelium of an ovariole of Oecanthus. Chromic acid 

 preparation. X300. 



Fig. 9. Yolk nucleus fresh in chromic acid, Beale's carmine. X 8001 



Fig. 10. Five yolk nuclei from a fresh preparation of an Oecanthus egg. 



Figs. 14-17, 20. Nuclei of serosa cells treated while living with acetic-acid carmine. Fig. 20 shows the 

 cell wall. 



Figs. 18, 19, 21, 22. Free cell elements from the yolk of an egg of Oecanthus in which the germinal 

 band was formed. They are the nuclei of the yolk cells. Fresh in osmic acid, stained in Beale's carmine, 

 mounted in glycerine. X 800. 



Fig. 23. Section of an unfecundated egg. HO. alcohol solution, neutral carmine. X 15. 



Fig. 24. Part of a section through an ovarian follicle of Oecanthus, prepared in hydrochloric alcohol 

 stained in picro-carrnine, benzole-balsam. X 560. 



Fig. 25. Transverse section of the germarium of Oecanthus. X 560. 



Figs. 26, 28-30. Sections of an ovariole of Oecanthus passing through the germinative vesicle ; from a 

 dissection in sodium chloride, stained in picro-carrnine, mounted in balsam and benzole. X 560. 



Fig. 27. Section of a young germinative vesicle extracted from its follicle. X 560. 



Fig. 31. Transverse section of an egg of Oecanthus after the appearance of the blastoderm and yolk 

 cells. X 65. Hydrochloric alcohol, alum carmine. 



Fig. 32. Section through the abdominal region of an embryo after the complete closure of the dorsal 

 wall. The section passes through the ovaries of both sides. X 125. 



Fig. 33. Section through the dorsum of an embryo before the closure of the dorsal vessel. The heart is 

 seen as two cavities in the ascending edge of the inesoblastic plates. X 500. 



Fig. 34. Cross section after the appearance of the fully formed dorsal vessel. X 100. 



Fig. 35. Section through the dorsum before the union of the two mesoblastie plates. 



Fig. 36. Section through the dorsal vessel in the thoracic region. X 250. 



Fig. 37. Section of the stomodaeum near the mouth. X 125. 



Fig. 38. Mesodermic structures from the body cavity of the same individual from which fig. 41 was 

 taken. These structures may possibly be the homologues of the segmental organs of worms. X125. 



Fig. 39. Frontal section of the nervous cord in the maxillary and mandibular region, showing the fusion 

 of three pairs of ganglia to form the suboesophageal ganglion, x 125. 



Fig. 40. Section of the ventral nerve cord in the abdominal region. X 250. 



Fig. 41. Section through the maxillary region of an embryo with a fully formed dorsal vessel. The 

 nervous system is cut across in four places. X 65. 



Fig. 42. Section of the egg of Oecanthus with a young blastosphere of Teleas in situ. From an osmic- 

 acetic acid, picro-carrnine, balsam preparation. X 100. 



Figs. 43-46. Nuclei from the follicular epithelial cells of an ovariole of Oecanthus. Osmic and chromic 

 acid, Beale's carmine. X 1000. 



Fig. 47. A yolk nucleus exhibiting interesting conditions of nucleolar structure. X 160. 



Figs. 48-50. Same as figs. 43-46. 



PLATE XXII. 



Fig. 1. Longitudinal section of an embryo shortly after revolution. The serosa cells by a process of 

 degeneration set free their large nuclei ; these pass into the mesenteron and the body cavity and there 

 undergo various changes. By an endogenous process each nucleus in the body cavity furnishes from two 

 to three nuclei which, on liberation from the membrane of the mother nucleus, become blood corpuscles. 

 In this stage the sexual organs are seen as a pair of elongated cell masses in connection with the heart 

 X65. 



Fig. 2. One of the nuclei from the fibroijs portion of the brain, showing its relations to the fibres, x 560. 



Fig. 3. One of the serosa nuclei from the body cavity. X 250. 



Figs. 4 and 5. Two stages in the development of the sexual organs. Fig. 4 represents the cell mass 

 before it begins to elongate. Fig. 5 represents the same after taking on the general shape of the future 



