OF OECANTHUS AND TELEAS. 279 



Fig. 14. Several spindle-shaped ectoderm cells from near V, fig. 13. Under a low power the large oval 

 or spherical nuclei are easily mistaken for cells. X 560. 



Fig. 15. A slightly oblique, transverse section through the anterior part of the brain of an individual 

 near the stage figured in pi. 19, fig. 5. Osmic acid, picro-carmine, balsam preparation, x 125. 



Fig. 16. Section through the eye at this stage, x 250. 



Figs. 17, 18, 19 and 20. Nuclei. Fig. 19. An endodermic nucleus. The others are nuclei from ovarian 

 epithelium of Oecanthus. 



Figs. 21, 22. Surface view and optical section of a blastosphere of Teleas in which the germinal band 

 has made its appearance. Shading in fig. 21 diagrammatic, x 100. 



Fig. 23. Optical section of a younger blastosphere. No cells are seen except those composing the 

 single-layered wall, x 125. 



Fig. 24. Optical section of a blastosphere with the primitive fold partly differentiated, kf, the head 

 region of the fold. M, a patch of mesoderm cells immediately beneath the ectoderm. X 125. 



Pig. 25. An unknown parasite found in the egg of Oecanthus niveus. h, the head end lying in contact 

 with the vitelline membrane. The body wall in the abdominal region was pushed out into three finder-like 

 processes. X 100. 



Figs. 26-30. Different views of the same blastosphere in the uninjured egg of Oecanthus. Figs. 27 and 

 28 are optical sections of the blastosphere in a plane grazing the upper surface of the germinal band ; 

 fig. 26. frontal (ventral) view of the germinal band; fig. 27, lateral view; tig. 28, an oblique dorsal 

 view. In fig. 29 the posterior termination of the germinal band is shown. Fig. 30, nearly the same as 

 fig. 29, but more oblique to the dorso-ventral axis. 



Fig. 31. A young blastosphere in its spherical mass of protoplasm, x 125. 



Figs. 32, 33. Blastospheres on the surface of which the primitive fold has appeared. The segmentation 

 cavity is partly filled by the mesodermic cells. X 125. In fig. 33 amoeboid cells are shown. 



Fig. 34. Ectodermic cells from different blastospheres. A. treated with osmic-acetic acid solution followed 

 by picro-carmine ; B. a single cell much larger than the others. Acetic acid carmine, glycerine preparation; 

 C. surface view of cells in situ. Beale's carmine, glycerine preparation; D. from an acetic-acid carmine, 

 glycerine preparation. All X 250. 



Fig. 35. A section of the blastosphere figured in pi. 21, fig. 42. X 800. The thinning is probably caused 

 by reagents. 



Fig. 36. Blastosphere collapsed by reagents in a manner resembling a gastrular invagination. X 125. 



PLATE XXIV. 



Fig. 1. An egg of Oecanthus with the three stages of Teleas in situ. X 30. 



Fig. 2. Side view of a well advanced first, or spindle-shaped, larva. There is a third prominence between 

 the frontal and mouth promontories. Four of the teeth at the base of the caudal appendage are arranged 

 in pairs. There are five incomplete girdles of spines. Osmic acid preparation. X 125. 



Figs. 3 and 4. Two views of a cylindrical larva near the stage shown in figs. 8 and 9. X 125. 



Fig. 5. Cephalic portion of a spindle-shaped larva. The frontal process is seen to be filled with gran- 

 ular protoplasm ; the mandibles and their muscles are well developed. Acetic acid preparation. X 500. 



Fig. 6. Ventral view of the same showing the manner in which the oral muscles radiate from the mouth 

 opening. On either side the body are seen the cup-shaped organs. X 500. 



Fig. 7. Side view of the cephalic portion of another larva showing the segmental constrictions in the 

 course of the enteric canal of this part. X 125. 



Figs. 8 and 9. Side and ventral view of another larva. The mesenteron and stomodaeum have not yet 

 united. Behind the enteric mass of cells is seen the germ of the sexual organs. The ventral band is seen as 

 a thickening of the hypodermis limited to the middle of the larva. X 125. 



Fig. 10. End of the abdomen of another larva, bearing the caudal appendage and seven, short, stout 

 spines. The hypodermic nuclei indicate the termination of the cell elements in this region. The caudal 

 appendage is filled with a finely granular protoplasm and at its tip is covered with bristles. X 800. 



Fig. 11. View of the enteric and sexual tract of a larva near the same degree of development as those 

 shown in figs. 3 and 8. X 125. 



Fig. 12. A larva with three greatly developed spines. They are placed between the girdles of bristles 

 and are nearly equal in size to the caudal spine. X 65. 



