ORGANIZATION AND CELL-LINEAGE OF ASC1DIAN EGG. 11!) 

 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 Oynthia (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 anil XII, lixed and stained eggs of Citmn hitextintdk. The figures of the 

 living eggs of Cynthia i plates I-V) were drawn at the stage level under Zeiss Apochromatic 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 study of prepared material. The figures of plates VI-XII, with the exception of figs. 61-75, 

 were drawn at the stage level under Zeiss Apochromatic Obj. 3 mm., Oc. 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 

 nun., Oc. 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 plates 

 II-V. 



A. 

 a.p.- 

 bp, 

 ch.- 

 cn.- 

 c. p.- 

 Cr.- 



Cr. s, 



D.- 



end.- 



f. c- 



g. v.- 

 kp.- 



mb.- 



m'ch.- 



ms.- 



n.- 



n. p.- 



Reference 



-Anterior. 



-Animal pole. 



-Blastopore. 



-Chorda 



-Chorion. 



-Clear protoplasm. 



-Crescent of mesodermal substance (yellow 



in Cynthia). 

 -Substance of crescent. 

 -Dorsal. 

 -Endoderm. 



-Follicle cells (outside of chorion). 

 -Germinal vesicle. 

 -Karyoplasm (achromatic substance from 



nucleus). 

 -Thick membrane which becomes chorion. 

 -Mesenchyme. 

 -Muscle cells. 

 -Nucleus. 

 -Neural plate. 



Letters. 



nl. Nucleolus. 

 n. t. Neural tube. 



P. Posterior, 

 p. b. Polar body. 



1 p. b. First bolar body. 



2 p. b. Second polar body. 



p. 1. Peripheral layer of protoplasm. 



1 P. S. First polar spindle. 



2 P. S. Second polar spindle. 



Sn . Sperm atozoon . 

 t. c Test cells. 

 V. Ventral, 

 v. end. Ventral (caudal) endoderm. 

 v. p. Vegetal pole. - 

 y. h. Yellow hemisphere of egg. 



' yk. Yolk. 



z Zwischenkorper (mid-body). 



n. Sperm 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 left posterior quadrants. From the 8-cell stage 

 onward the cells of the eudodermal hemisphere are designated by capital letters, those of the ectoder- 

 mal hemisphere by lower case. The first exponent indicates the cell generation, counting the unseg- 

 mented egg as the first ; the second exponent the position of the cell relative to the animal and vegetal 

 poles, cells which lie nearest the vegetal pole having the lowest exponent, those farthest away (nearest 

 the animal pole) having the highest. See p. 37. 



