No. 3-] THE EMBRYOLOGY OF A TERMITE. 5 19 



Fig. 13, the limits of this diminishing area have drawn well in 

 toward the center and away from the lateral margins of this 

 portion of the ventral surface. In PI. XXX, Fig. 18, the germ- 

 disc hardly covers one-half of its extent in PI. XXX, Figs. 12 

 or 13. 



The appearances are not at all what would be expected from 

 a simple cell multiplication in a restricted area. In such a 

 case the growing disc should, it seems, be formed from the 

 coalescence of several areas multiplying around separate cen- 

 ters, or should spread out on all sides as its cells multiply 

 around a single center. As the figures show, the disc is here 

 formed by a steady contraction of a primarily extensive area 

 toward a central point. 



The fact that, at even so late a stage as one showing the 

 amnio-serosal fold, the nuclei of the disc are of the same size as 

 those in the surrounding blastoderm, perhaps lends some sup- 

 port to the above contention ; since we should expect a rapid 

 multiplication vi^ithin a restricted area of the blastoderm to 

 produce a mass of cells in that region of smaller size than on 

 the surface elsewhere. In the Termite, during this period, the 

 nuclei of the blastoderm in the whole posterior half of the Q.g% 

 appear to divide with about the same rapidity. The process of 

 concentration, which draws the cells together to form the disc, 

 is accompanied by a steady multiplication of the cells about to 

 be incorporated in it, but the nuclei of the rest of the blasto- 

 derm divide also. The position of the embryonic disc is conse- 

 quently not marked by nuclei smaller than those elsewhere on 

 the blastoderm, in the stages we are considering. 



The first rudiment of the embryo is certainly not formed 

 around a number of discrete centers, as is claimed for some 

 decapod Crustacea and certain insects. The concentration lead- 

 ing to its first formation is, from the start, most apparent in the 

 posterior portion of the disc. The posterior border becomes 

 sharply defined at an early stage, as the cells draw together in 

 concentric rows from the posterior pole. The lateral edges are 

 next involved ; but much later, when the disc is otherwise well 

 outlined and its cells are quite closely crowded, the nuclei of the 

 anterior end have not yet drawn together (PI. XXX, Figs. 18 and 



