No. 2.] EMBRYOLOGY OF THE AMERICAN LOBSTER. 22$ 



erably larger than that of the immediately preceding stage, it 

 has not otherwise materially changed, save that it ordinarily 

 contains only one nucleolus. The nucleolus, moreover, is thick 

 walled, appearing in section as a deeply stained ring, with its 

 centre often relatively free from chromophilous substance. In 

 the section Fig. n, it is interesting to note that the nucleoli 

 occupy an eccentric position, each being confined to the left 

 half of its respective nucleus. 



When the egg-cells are about one-half grown, as on PL XVI, 

 Fig. 1 1, the protoplasmic halo becomes still more prominent, 

 and, in some cases, minute particles of pigment are found 

 immediately surrounding the nucleus, the signification of which 

 I will not attempt to give. The nucleus has several times the 

 volume of that of the preceding stage. The outer portion of 

 the cell has become densely filled with fat and plasma vacu- 

 oles, or vesicles, which may be more clearly seen in the consid- 

 erably enlarged drawing, Fig. 7, Ft.vs and P.vs. The fat vacuoles 

 are of varying size. At the right, a smaller one will be seen in 

 the act of emptying itself, probably the result of the action of 

 hardening reagents. The plasma vacuoles now show nuclei, 

 though not in all cases ; and in larger vacuoles, nucleoli are to 

 be found. We have then cellular (?) bodies within the so-called 

 egg-cell, though the " plasma cells " do not take up stain so in- 

 tensely as do the cells of the follicular epithelium. Two nuclei 

 of the latter cells are to be seen at fe. 



At the present stage in the development of the egg-cell, the 

 primary egg membrane may be distinguished. At pe-m, Fig. 

 11, it is seen to enclose a fat vesicle or globule that is leaving 

 the egg. 



As growth continues, the perinuclear halo — in early stages 

 never a network as it is in Eupagurus — leaves its primary posi- 

 tion, and, working through the yolk, increases its extent, while 

 approaching the periphery of the egg. 



A very marked change now comes over the yolk. Heretofore 

 made up of more or less homogeneous masses of varying size, 

 it now becomes broken up into small spheres which are not 

 visibly bound together. As in younger eggs, the fat vacuoles 

 abound ; but the plasma vacuoles have become altered. The 

 latter are represented by interstitially lying chromatin bodies, 

 probably supended in a network of protoplasm and confined to 



