EMBRYOLOGY. 85 



figs. 1, 2) was the period of formation of the primitive 

 band. I could not detect any eggs with blastodermic 

 cells or a blastoderm fully formed. Fig. 2 represents 

 the primitive band lying upon the outside of the yolk 

 next to the chorion, and divided into the external 

 tegumental layer (t) and the inner or muscular layer 

 (m). The two ends of the primitive band meet at a, 

 the band thinning out so as to be of an imperceptible 

 thickness just before a (fig. 1), where there is a clear 

 space and an infolding (a) of the primitive band, which 

 seems to be the place of meeting of the anterior and 

 posterior end of the germ. A little later the fold grows 

 deeper (as at b, fig. 2), and a seems to indicate the 

 rudiments of the cephalic lobes. The exact mode of 

 origin of thesejobes (Scheitelplatte of Zaddach) I did 

 not observe. 



" At a more advanced period of development the 

 primitive band, now, more properly speaking, the 

 primitive body-walls, is clearly defined, and is more 

 homogeneous, the small cells previously scattered 

 through its substance (as in fig. 2) having disappeared. 

 This stage is signalised by the appearance of the 

 primitive arthromeres or segments of the body (pro- 

 tozoonUes of Claparede). They originate just as they 

 do in the Phryganidce, according to Zaddach. They 

 arise six in number (fig. 3), representing probably 

 three cephalic and three thoracic segments (unless the 

 fourth is the second maxillary arthromere, which more 

 extended observations may prove to be the case). It 

 will be noticed that they arise on the opposite side of 

 the egg from the fold a, so that the cephalic lobes 

 (p /) extend from a around to I. The central 

 portion, or muscular layer of the egg, is now more 

 homogeneous than before, the fat-globules having 

 disappeared in the centre of the egg. Plate III, 

 figs. 4 and 5, represent the germ farther advanced 

 and the budding out of the appendages. The cephalic 

 lobes are, as in fig. 5, quite clearly indicated, and the 

 rudimentary appendages, in most cases, well shown. 



