No. 3-] THE EMBRYOLOGY OF A TERMITE. 527 



the cephalic region is slightly emarginated. On either side it 

 extends up on the yolk as a broad lobe with rounded borders. 

 Such is the appearance of the embryo just before segmentation. 

 {See also next section for a description of PI. XXX I ^ Fig. 28, of 

 this stage.) 



Changes in the Mesoderm and Amnion during the 

 Elongation of the Germ-Band before 



its Segmentation. 



PI. XXXI, Fig. 36, is a sagittal section through a stage in 

 the elongation of the embryo, slightly older than that of PI. 

 XXXI, Fig. 24, when the anterior end has broadened and 

 become square, as in PI. XXXI, Fig. 26. Compared with 

 PI. XXXI, Fig. 35, this whole embryo is decidedly longer. 

 The amnion appears thinner, its cells are becoming arranged 

 in a single layer, especially at the anterior end. As the germ- 

 band has grown posteriorly, the mesoderm has multiplied by a 

 division of its own cells and followed back, not quite so rapidly 

 as the ectoderm, becoming a flattened pad of cells beneath 

 this layer. (The mesoderm cells are well seen as a flat layer 

 beneath the entire width of a germ-band of this age dissected- 

 off and stained for a surface view.) The mesoderm extends 

 no further forward than in section, PI. XXXI, Fig. 35, but the 

 ectoderm of the anterior end of the embryo has pushed out in 

 front to a slight degree. 



PI. XXXI, Fig. 25, is a side view of an egg of about the 

 same age as that sectioned in PI. XXXI, Fig. 36. The embryo 

 occupies a peculiar position for one of this stage, ordinarily 

 being found on the ventral surface as shown in the younger 

 egg (PI. XXXI, Y\g. 24). It appears to have slipped back into 

 the exceptionally large space between the chorion and yolk. 

 It gives a good idea of what is shown in the section, PI. 

 XXXI, Fig. 36, just described. Note the inflated amniotic 

 cavity. The amnion is seen partly in optical section where it 

 passes into the ectoderm posteriorly, and anteriorly where it is 

 drawn out into a thin membrane. On its surface the cells 

 form a mosaic. The mesoderm cells lie loosely beneath the 



