100 BULLETIN OF THE 



Fig. 23. Au enlarged view of the head region, at about the same stage as the pre- 

 ceding. 



PLATE V. 



Fig. 24. A portion of the surface of a living egg of Agelena nctvia, after the division 

 of the blastema into polygonal areas. Several of the yolk corpuscles 

 have shifted from their original positions, and therefore no longer 

 coincide with the areas. X 163. 



" 25. Polygonal areas of the blastema and underlying yolk globules more 

 highly magnified; from a living egg. X 440. 



" 26. Primary blastodermic cells before they become regular in form and size; 

 from a living egg. X 163. 



" 27. A portion of the blastoderm on the third day (temperature 23° C) of de- 

 velopment ; from a living egg. X 163. 



" 28. A little more than one half of the section of an egg, containing only one 

 nucleus, the first segmentation nucleus; siiowing blastema {hi'.), 

 nucleus (nl.), and yolk corpuscles (yk.)- X 110. 



" 29. First segmentation-nucleus with the surrounding protoplasm highly mag- 

 nified, showing also a rapid diminution in the size of the yolk cor- 

 puscles in its vicinity. X 330. 



PLATE VI. 



Fig. 30 Enlarged view of a portion of Fig. 28, showing the blastema (W.) and 



underlying y^lk corpuscles (yk.)- 

 ' 31, 32. Isolated peripheral yolk corpuscles, to which portions of the blastema 



are attached. 

 " 33. Isolated yolk corpuscle with a vacuole, which in turn contains a rounded 



yolk globule. 

 " 34. Section through the nuclei of an egg in the two-cell stage, showing the 



two groups of yolk columns (Deutoplasmasaulen). X 110. 

 " 35. One of the deep internal cells, surrounded by yolk. 

 " 36. A nucleus containing a central vacuole ; from an egg in the two-cell 



stage. 

 " 37. A migrating cell that has just reached the periphery, abutting on tlie 



blastema (W.). 

 " 38. Detached portion of the blastema viewed from within, showing depres- 

 sions into which the yolk corpuscles fit. 

 •' 39. Section of an egg passing transversely through the primitive cumulus in 



the region of its greatest width. X 110. 



PLATE VIL 



Fig. 40. Radial section of two blastodermic cells. 

 " 41. Section passing sagittally through the primitive cumulus. X 110. 

 " 42. A blastodermic cell in the process of division, with " interzonal filaments." 



