No. I.] THE EMBRYOLOGY^ OF LIMULUS. 45 



In from forty-two to forty-eight hours the eggs, as they he in 

 the dish, show on their upper surfaces the first traces of segmen- 

 tation of the yolk. In this there is no regularity as to the direc- 

 tion of the furrows nor uniformity in their extent. At first 

 the furrows are clean cut, with well-defined margins and some 

 depth, but soon they become shallower, and the margins and bot- 

 toms become irregular by the formation of numerous yolk spheres 

 of varying size (Figs. 10, 1 1). Gradually the furrows flatten out, 

 and the yolk spheres become merged in the general yolk of the 

 surface, and the &gg is as smooth as before. In from four to six 

 hours this process is repeated, the spaces between the furrows be- 

 coming smaller and the furrows embracing more of the ^g^ than 

 before (Fig. 12). This is repeated several times, until at last 

 the whole surface is included in the segmentation (Figs. 13, 14). 

 At each of these divisions there are at first the same clean-cut 

 furrows followed by the same irregularity, and eventually by the 

 apparent obliteration of the planes of segmentation. 



Sections plainly show (Fig. 15) that this is a true segmenta- 

 tion of the yolk, the result being to divide the whole ^gg into a 

 series of cells, each consisting of a mass of yolk (Fig. 18) with 

 a central nucleus. It is also apparent that therewith is con- 

 nected the appearance of the nuclei at the surface of the &gg 

 and the formation of a blastoderm (Fig. 15). In the projection 

 of an &gg of forty-eight hours (Fig. 16) twenty-six nuclei were 

 seen. A little later (2^ days) a higher power shows some inter- 

 esting phenomena. The nucleus is surrounded by an amoeboid 

 mass of protoplasm, sending processes into the surrounding yolk, 

 while the planes of segmentation, as well as the external surface 

 of the ^gg, are covered with a thin layer of faintly staining pro- 

 toplasm (Fig. 17), apparently the blastema of the earlier stages. 

 At the time when these furrows seem to disappear {supra), this 

 protoplasm regains the surface, but the furrows themselves 

 remain, and eventually the whole Q.gg is divided into nucleated 

 yolk cells (Fig. 18). 



At first the central portion divides as rapidly as the peripheral, 

 and in each portion of the Q.gg the cells are about equal in size ; 

 at last, however, the central cells enter upon what may be called 

 a resting stage, which condition persists until after the beginning 

 of a free-swimming life. Their divisions occur at infrequent 

 intervals, and the differences in size, from the appearance of 



