Nos. 4S5-456-] FASCIOLARIA. 



873 



branch embryos, but they do not reach such large dimensions or 

 become such conspicuous objects in any other described forms 

 as in Fasciolaria. They are called " sub-velar masses " in my 

 paper of '85, and are shown in Figs, i, 2, 3, 4, and 5. They 

 are very early of development and are already conspicuous 

 organs when the shell gland first shows. The velum subse- 

 quently arises and spreads out over them. In the earliest 

 embryos the ectoderm cells of the area on each side of the 

 mouth undergoes a peculiar change (Fig. 3), the boundaries of 

 the cells cannot be seen, vacuoles 

 of various sizes appear in the cyto- 

 plasm, and some of the larger vacu- 

 oles push the nuclei aside compre^^s- 

 ing the nucleus, much as m the fat 

 cells of vertebrates. This is the 

 first step in the development ot the 

 larval kidney. The nuclei at this 

 time still show mitosis, two of the 

 cells of the figure are in stages of 

 active karyokinesis, there is no evi- 

 dence as yet of amitosis. As the 

 accumulation of material within the 

 cell goes on, the outer end is pushed 

 up above the general level of the 



ectoderm and becomes the swollen 



organ we see. The cells become ^^"^''J^'.ll'^Vf'n^^ ^ 

 wedge-shaped, each retains its place sIk vvn.g tnst st ii,.s m ti e f r 

 on the ectoderm by its base, the 



Cytoplasm is pushed out into the outer end ol the cell, 

 becomes rounded there as if through the influence ot pi 

 from within. The content of the cell is chiefly a matciial 

 in life is fluid and highl) refiactuc, but il 1^ toii^ulatcd 1 

 servative reagents; it is faintly stamablc and not (ll^^()l\ 

 absolute alcohol or oil. I he cytoplasm at the ouici uul 

 cell (Fig. 4) contains one or more nuclei. Ihc relation < 

 cells to the general ectoderm is sh(.)wn m tig. 4. the or 

 considerably constricted at its base. 



There are no evidences of cell dnision among the older 



