PHOTOGENIC ORGANS OF LAMPYRIDS 173 



A few cells may protrude into the amniotic cavity (fig. 33), at 

 the point where the closure of the folds is effected. The cells 

 of the blastoderm (the peripheral cells shortly separated from 

 the embryo and commonly termed the serosa) have fairly dis- 

 tinct walls and are fusiform-flattened. The yolk, Y, which stains 

 very deeply, is massed into subspherical bodies about 0.6 to 6 

 micra in diameter, and the vitellophags are much less evident, 

 though now probably more numerous. Yolk granules may occur 

 in the cells of the germ band as well as in the blastoderm. 



Before gastrulation, the embryo both lengthens and broadens 

 considerably, though its dorso-ventral thickness increases but 

 little. Heretofore quite straight in its long axis, it curves dor- 

 sally and thus partially embraces the yolk-mass. It appears 

 constricted before its middle, because the anterior portion has 

 been broadened and furrowed to form the procephalic lobes (figs. 

 35 and 36). It is now about 263 micra in its straight length. 

 It has become separated from the serosa, and, sinking towards 

 the center of the egg, becomes a germ band of the immersed 

 type. (Quite late in development, the amnion and the serosa 

 come in contact in a comparatively small area in front of the 

 mouth, (fig. 52) ). Here the amnion and the serosa are sepa- 

 rated from each other by an intermediary mass of yolk. This 

 condition is represented in a later stage in figures 51 and 52. 

 It seems that the immersed type of germ band is unusual in the 

 Coleoptera. According to Korschelt and Heider ('99) the germ 

 band of Coleoptera ". . . . is superficial and is grown 

 over by the forward extension of a caudal fold and paired cephalic 



folds The posterior end of the germ band on the 



contrary develops entirely according to the invaginated type." 

 But later, by shifting, the germ band becomes totally superficial. 

 Such a condition is found in Hydrophilus and Lina (Graber), 

 Chrysomela (Strindberg), and probably in others. 



Figure 37 shows a later stage of development. Segmentation 

 is not yet apparent, but the embryo has greatly increased its 

 size and curvature, for it now measures 390 micra in its full 

 length. The cephalic lobes, P, are wide and separated anteri- 

 orly by a deep cleft. The amnion, A, forms a stout envelope, 



