EXPLANATION OF PLATE Til— Continued. 



germ-bands appear as two thickened lateral marE^ins of the germinal disc. 

 The place of the future mouth (/>«) is seea in the centre of the cephalic 

 mass ; this point marks nearly the centre of the four primary ectoblasts. 

 The pharyngeal clefts (oc) are marked by slight depressions at the line of 

 junction of the germ-bands with the cephalic portion. (36 h.) 



Fig. 39. — The same from below. The eutoplasts have increased ia 

 number. 



Fig. 40. — Only the thickened margins of the germinal disc are repre- 

 sented. The four superficial lines of cells produced by the neuroblasts give 

 the bands a striated appearance. The fore ends of the bands rise above the 

 level of the cephalic portion, as is plainly seen when the egg is tilted. The 

 pharyngeal clefts (pc) are now nearly parallel with the linear depression 

 leading backward from the mouth {Fa). (42 h.) 



Fig. 41. — The anterior ends of the germ-bands are already in contact, 

 and the pharyngeal clefts are nearly at right angles to the postoral depres- 

 sion, which is seen to be continuous with the primitive groove {p.gr). 

 (48 h.) 



Fig. 42. — The same, tilted on the hind end, to show that the ventral 

 blastomere (c) is being driven up between the lateral blastomeres {a, b). 



Fig. 43. — The same seen from behind. The entoplasts, which are not 

 represented in the following figures, are quite numerous, and scattered over 

 the entire surface of a, b, and c. 



Fig. 44. — Seen from behind. The germ-bands are about two thirds 

 closed. The ventral blastomere (c) is now wider on the dorsal than on the 

 ventral side. (60 h.) 



Fig. 45. — The same, seen from before. The raetameric formation already 

 begun. 



Fig. 46. — The germ-bands most closed. The pharyngeal clefts have 

 encircled the pharyngeal portion. The ganglionic formation is quite dis- 

 tinct. A few hours before hatching. (72 h.) 



Fig. 47. — The same, xy is seen as a dark area in the right side. 



Fig. 48. — The neuroblasts, which are much reduced in siz3, form a semi- 

 circle around the posterior enHs of the fully closed bands. The two meso- 

 blasts appear as ill-defined dark spots, lying near the surface of a and c. 

 (One day old.) 



Fig. 49. — The same, seen in profile. The segment-cells are seen between 

 each metamere. 



Fig. 50. — The pharynx protrudes a little, xy is less distinct. The 

 septa are lengthening towards the dorsal side. The boundary lines of «, b, 

 and c have disappeared. (3 days old.) 



Fig. 51. — The same, from the ventral side. 



Fig. 52. — The dorsal side is still shorter than the ventral. The three 

 main divisions of the digestive tract with their cteca are now recognisable. 

 The septa have not yet reached the dorsal side. (6 days old.) 



Fig. 53. — Of the same age, but farther advanced. 



Eig. 54. — Also of the same age, but still farther advanced. The dorsal 

 and ventral sides are of about equal length. 



Fig. 55. — The worm has nearly attained its definitive form. The eyes 

 appear about this time as orange-coloured spots. (7 days old.) 



