BIGELOW: EARLY DEVELOPMENT OF LEPAS. 143 



EXPLANATION OF PLATES. 



The figures of Plates 1-10 were drawn from the eggs of Lepas anatifera, and 

 those of Plates 11 and 12 from L. fascicularis. 



An Abbe camera lucida was in every case used in sketching the eggs. The 

 figures of Plate 1, and Figures 57, 63-65, 74-77 were drawn at a magnification of 

 about 220 diameters ; all others in Plates 1-10 at about 365 diameters. The fig- 

 ures of Plates 11 and 12 are magnified about 210 diameters. 



All figures, except those of transverse sections, are so arranged that the posterior 

 end of the embryo, or the more pointed end of the vitelline membrane, is directed 

 toward the bottom of the Plate; in transverse sections the ventral side is toward 

 the bottom. 



Double-headed arrows are used in some of the figures to connect two cells of 

 common origin. 



The vitelline membrane has not been represented, except in Figures 1-17 and 

 94-97. 



Figures 1-30 and 95-99 are oriented by the axis of the vitelline membrane ; all 

 others by the axis of the embryo. 



The small circles without stippling indicate the positions of the oil spherules in 

 the yolk. Nuclei are distinguished by wavy lines, or by stippling, to represent 

 chromosomes. 



In Plates 2 and 3 a pale yellowish buff tint has been used to represent the more 

 finely granular and more " protoplasmic " portion of the egg and blastomeres. 



Plates 1, 4, 11, and 12 have been printed without tint. To aid in quickly dis- 

 tinguishing between the derivatives of quadrants a, 6, and c, all the blastomeres 

 of quadrant b in Figures 38-59, 61 are printed in stipple without tint, and in Figures 

 60 and 65 (Plate 7) the same method of designation has been employed to indicate 

 the cells (6 7<5 -6 7 ' 8 ) of this quadrant concerned in the formation of the secondary 

 mesoblast. 



In Plates 5-10 the pale yellowish buff tint has been employed to indicate the 

 blastomeres derived from quadrant d, the primary mesoblast (c/ 5 ' 2 and its descend- 

 ants) being distinguished from the other derivatives by receiving a stippling in 

 addition to the tint. In Plates 8-10 the tint has been restricted to d 4 ' 1 (entoblast) 

 and its derivatives. 



