438 



MEMOIRS OF TEE NATION^AL ACADEMY OF SCIENCES. 



percentage of increase of wandering cells between Stages ii and iii is double that of tbe embry- 

 onic cells. Between Stages iii and iv tbe increase per cent of wandering cells is less than that of 

 tbe embryonic cells, and np to this time cell disintegration is rnled out as a disturbing factor. 



£A. 



Fio. 12.— Curve showing diatribution of wunderiEK cells in Stage V (Early egg.nauplius) . (Compure Fig. 11, and lor details, see Table ' 

 I, Stage, II b.) E A, Embryonic area: Mo, Mouth. 



The second fact which was pointed out as characteristic of this stage, the distribution of the 

 yolk nuclei commensurate with that of the yolk itself, also points to the conclusion already reached. 

 This is well shown by two curves (Figs. 12, 13). In curve 13, which is constructed from a series 



Fl(i. 13.— Curve showing the distribution of wandering cells in Stage v, a. (v. Table I.) A, Anterior; P, rosterior. 



of transverse sections, we see that wandering cells are most abundant in the thoracic-abdominal- 

 fold region and in that which answers to the future heart. We also notice the forward extension 

 of migratory cells beyond the anterior edge of the optic lobes. In cut 12 the lateral extension 

 of the nuclei on either side the embryo is well shown. The mouth is involved in section No. 28, 



