96 NEW YORK STATE MUSEUM 



represented on plate 30, figures 2 and 3. It occurred in a small, 

 yellow larva and had a length nearly equal to that of the ninth 

 segment of the mother larva, its width being about one-fourth th( 

 diameter of the parent. This embryo is evidently in the morula 

 stage, it being composed of a rather indistinct mass of irregular, 

 closely placed cells, apparently with a slight infolding, the begin- 

 ning of the blastoderm. At the posterior extremity there is 

 group of nucleated, large, polar cells. The next stage observed, 

 though not photographed, was seen in larva Y. This embryo had 

 a length equal to nearly twice the diameter of the mother larva. It 

 was narrowly elliptical, with a length approximately three timej 

 its diameter and the polar cells, though visible, were not so evi- 

 dent as in the embryo described above. At its anterior extremity 

 there was a slight thickening, apparently the much reduced cells of 

 the corpus luteum. The median portion was occupied by a rathei 

 broad streak of dark, granular cells, bordered on either side and 

 at the extremities by lighter, small-celled tissue. A more advanced 

 stage is shown on plate 30, figure i, and plate 31. This represents 

 an embryo dissected from the large, white type of mother larva. 

 It shows a distinct darker ectoderm and a lighter mesoderm, the 

 anterior extremity having a conspicuous cap of large, dark cells. 

 Portions of the posterior extremity and of the middle of the same 

 embryo are represented still more enlarged on plate 31, figures i 

 and 2. The time required for the small embryos to migrate from 

 the region of the ovaries and develop to such an extent as de- 

 scribed above and thus produce a quiescent stage in the large, white 

 type of mother larva is approximately four to five days, much 

 appearing to depend upon the size of the mother larva and the 

 number of embryos present. The latter are perhaps most easily 

 seen when viewed by reflected light (pi. 23 fig. i, 2). The next 

 stage in the development is illustrated on plate 32, figure i. The 

 embryo has a distinct cephalic cap of dark-celled tissue, a well 

 defined germinal streak, the latter being broadly produced to one 

 side in the region of the anterior third. The same general condi- 

 tion, though in a more advanced stage and apparently from 

 somewhat different viewpoint, is illustrated on plate 32, figure 4, 

 and plate 33, figure 2, the dark ectoderm occupying one-third the 

 width of the embryo and extending from approximately the re- 

 gion of the sixth to the twelfth segments ; the cephalic cap persists 

 as before. This condition appears to be followed shortly, though 

 we have observed it somewhat clearly only in embryos developing in 



