465 



surface of this tube and the serosa Hes a mass of cells in an irregular 

 layer, of the same nature as those lying in the hollow on the ventral 

 surface. The axis of the rounded, tube-like, anterior portion of the 

 germ band does not coincide with the longitudinal axis of the entire 

 egg, but is anteriorly inclined towards the ventral surface. The hol- 

 lows on the dorsal and ventral surfaces give to the germ band and 

 the inner protoplasmic layer a somewhat slipper-shaped appearance 

 in longitudinal vertical sections, the heel beingr formed by the germ 

 band and the toe by the inner layer of peripheral protoplasm, the 

 longitudinal axis of the slipper lying diagonal to the longitudinal 

 axis of the egg. Encircling the toe of the slipper and extending for- 

 ward on the dorsal surface about half the length of the blastoderm 

 are the rather deeply-staining cells mentioned as occurring in this 

 position in the three-day stage, but the layer has pushed forward 

 farther on the dorsal side at this stage. Most of these cells contain 

 the bacteria mentioned above. At the anterior end of this layer on 

 the ventral surface occur the large vacuolated multinucleate cells 

 described above. The group of cells originating at the anterior end 

 of the ventral groove has increased greatly in size so that the anterior 

 end of the germ band now appears as a solid mass of cells. The 

 ventral groove and the cells of the middle plate have just about 

 reached the posterior end of the germ band. 



At the age of six days the germ band has grown backward on 

 the ventral side along the inner layer of peripheral protoplasm to 

 the most posterior place occupied by that layer in the region of the 

 middle of the egg near the posterior end (Fig. i6). It has grown 

 back as a layer several cells in thickness in the median line, thinning 

 out to a delicate one-celled layer laterally. Over the anterior half 

 this layer is continuous with the delicate one-celled layer extending 

 backward from the antero-dorsal part of the germ band, forming here 

 a dorsal closure of the embryo. This dorsal closure has not yet been 

 effected over the posterior part. The layer of inner peripheral pro- 

 toplasm now contains a great many more nuclei, so that it forms a 

 loose nucleated layer extending over the entire dorsal area and lying 

 just inside the delicate one-celled layer which is continuous with the 

 edges of the germ band. 



At the very posterior end of the germ band a significant change 

 is beginning at this stage. The germ band now extends back to 

 the point where the peculiar, large, multinucleate cells and the large 

 heavily-staining cells, mentioned as occurring at the posterior and 

 the postero-dorsal part of the blastoderm, begin. At this point the 

 germ band forms a knot-like thickening, and from this thickening 



