33 
154. TWELVE-CELL STAGE OF PHyYSA, showing the budding off 
of the second group of micromeres to the right. 
155. TWELVE-CELL STAGE OF LIMN4A, showing the budding 
off of second group of micromeres to the /eft. 
(N. B. The 1st and 2d groups of micromeres are always given 
off alternately to right or left, or vice versa.) 
Exhibit of Cytological Preparations. 
156-160. CHROMATIN AND ARCHOPLASM DURING FERTILIZA- 
TION, or union of the male and female hereditary elements, 
in eggs of the sea-urchin. Four stages: Magnified 1000 
diameters. Stained by “ iron hematoxylin method.” 
By Edm. B. Wilson (Biological Department, Columbia College). 
This exhibit shows that the dynamic cell-dividing Archoplasm 
substance is entirely derived from the male cell or spermatzoén. 
156a@. EGG OF SEA-URCHIN BEFORE FERTILIZATION. Section of 
ovarian egg of sea-urchin (Toxopneustes) showing the nucleus 
or germinal vesicle (the large clear vesicle) and the nucleolus or 
germinal spot (the round black body within the vesicle). With 
accompanying photograph magnified 1000 diameters, 
156d. FERTILIZATION OF SEA-URCHIN EGG. Egg of Toxo- 
pneustes, more highly magnified, showing the process of 
fertilization. The sperm nucleus (which has penetrated into 
the egg from the outside) appears as a small, black, conical 
body. Beside it is the star-shaped sperm-aster or archoplasm. 
The egg nucleus now appears as a small rounded vesicle. 
With accompanying photograph magnified 1000 diameters. 
156c. EGG OF SEA URCHIN PREPARING TO DIVIDE INTO TWO 
CELLS. Egg of Toxopneustes preparing for first division or 
cleavage, showing the “amphiaster,” each half of which will 
pass into one of the daughter-cells. With photograph 1000 
diameters. 
156d. CELL DIVISION OR SEGMENTATION INTO 16 CELLS. 
Segmenting of egg of Toxopneustes (16 cell-stage) in section 
showing the cleavage-amphiasters. With photograph 1000 
diameters. 
