ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 119 
EXPLANATION OF FIGURES. 
All figures represented in the plates were drawn with the aid of the camera lucida, Plates I-V 
represent the living eggs of Cynthia (Styela) partita, and the colors used are in no sense diagrammatic 
but are as nearly as possible those which appear in life; plate VI-X show fixed and stained eggs of the 
same species; plates XI and XII, fixed and stained eggs of Ciona intestinalis, The figures of the 
living eggs of Cynthia (plates I-V) were drawn at the stage level under Zeiss Apochromatie Obj. 4 
mm., Oc. 4, and are therefore magnified 250 diameters. With the exception of figs. 46-49 all the 
details shown in these drawings were observed in living eggs without reference to fixed and stained 
material; in the figures specified certain cell outlines were added to the drawings of the living eggs 
after a ага of prepared material. Тһе figures of plates VI-XII, with the exception of figs. 61-75, 
were drawn at the stage level under Zeiss Apochromatic Obj. 8 mm., Ос, 4; in the process of repro- 
duction they have been reduced about one-fifth so that as they now appear they represent a magnifica- 
tion of about 266 diameters. Figs. 61-75, plate VI, were drawn under Zeiss Apochromatic Obj. 1.5 
mm., Ос. 4, and therefore represent a magnification, after reduction, of about 535 diameters. The 
chorion and test cells, though present in most of the eggs drawn, have been omitted from all the 
figures, except those of plates I, VI and VII; the chorion, without the test cells, is shown in eee 
II-V. 
REFERENCE LETTERS. 
A.—Anterior. 
a.p.—Animal pole. 
bp.—Blastopore. 
ch.—Chorda 
en,—Chorion. 
с. p.—Clear protoplasm. 
Cr.—Crescent of mesodermal substance (yellow . 
in Cynthia). 
Cr. s.—Substance of crescent. 
D.— Dorsal. 
end.—Endoderm. 
f. c.—Follicle cells (outside of chorion). 
g. v.—Germinal vesicle. 
kp.—Karyoplasm (achromatic substance from 
nucleus). 
mb.—Thick membrane which becomes chorion. 
m'ch.—Mesenchyme. 
ms.— Muscle cells. 
n.—Nucleus. 
n. p.—Neural plate. 
nl,—Nucleolus. 
п. t.—Neural tube. 
P.— Posterior. 
p. b.— Polar body. 
1 p. b.— First bolar body. 
2 p. b.—Second polar body. 
p. ].— Peripheral layer of protoplasm. 
1 P. S.—First polar spindle. 
2 P. S.—Second polar spindle. 
Sn.—Spermatozoon. 
t. c. — Test cells. 
V.— Ventral. 
у. end.— Ventral (caudal) endoderm. 
v. p.— Vegetal pole. 
y. h.— Yellow hemisphere of egg. 
yk.—Yolk. 
z.— Zwischenkórper (mid-body). 
Ъ n.—Sperm nncleus. 
9 n.— Egg nucleus. 
NOMENCLATURE OF “CELLS. 
A—Anterior half of egg ; B—Posterior half; AB— Right half; AB— Left half; A and A—Right | 
and left anterior quadrants; B and B—Right and d left posterior quadrants. From the 8-сей stage 
onward the cells of the endodermal hemisphere are designated by capital letters, those of the ectoder- 
mal hemisphere by lower case. The first exponent indicates the cell , counting the unseg- 
mented egg as the first; the second exponent the position of the cell relative to the animal and v 
poles, cells which lie nearest the vegetal pole ‚ч the lowest кен those farthest away (nearest 
the animal pole) having the highest. See p. 3 
