404 PROCEEDINGS OF THE ACADEMY OF [April, 
Fig. 48.—Same egg as fig. 45, lateral view of C. quadrant. 
Fig. 4 49.—Lateral view of D quadrant in egg of about 86 cells. 2d! is 
dividing lxotropically ; Saat and 2d?!” have divided dexiotropically. 
Fig. 50.—Lateral view of same egg as fig. 49, showing A quadrant. 
Pirate XXVIII, Fig. 51.—D quadrant, a lateral view. Me! and Me? all dividing 
bilaterally. 
Fig. 52.—Lateral view, B quadrant of same egg as fig. 49. 
Fig. Pet apes pole view of egg of about 86 cells. The “‘apical’”’ (la'!!—- 
1d‘) and “peripheral” (1a!!?-1d"?) rosettes have been formed by 
leotropic cleavages. 
Fig. 54.—Same egg as fig. 51, seen from side (C quadrant). 
Fig. 56.—Upper pole view of ‘an egg of approximately 106 cells. The basal 
cells, lay 1b, 1c, have divided; 1d'! is dividing with spindle 
transverse to posterior arm of cross. The two inner posterior 
trochoblasts (1c, 1d”) are dividing bilaterally. 
Fig. 57.—Vegetative pole view of same egg as fig. 56. Completed division 
of Mel, Me? into M'e!, M’e? and m!z!, m?z?. 
Fig. 58. —Same egg as fig. 56, showing A and D quadrants on lateral view. 
Fig. 59.—Same egg as fig. 56, principally B quadrant. 
PuaTe XXVIII, Fig. 60.—Same egg as fig. 56, lateral view of C quadrant. 
Fig. 61.—Lateral view, D quadrant, same egg as fig. 56. 
Fig. 62.—Upper pole view of egg slightly older than last series (over 115 
cells). All the interior trochoblasts have divided, and the completed 
transverse division of the basal cell of the posterior arm of the cross 
is shown. 
Fig. 63.—Same egg as fig. 62, showing A quadrant on lateral view. 
Fig. 64.—Lateral view, same egg as fig. 62, B quadrant. 
Fig. 65.—Lateral view, same egg as fig. 62, C quadrant. 
Fig. 66.—Lateral view, same egg as fig. 62, D quadrant. , 
Fig. 67.—Egg of about 125 cells, lateral view, C quadrant. 

Puath XXIX, Fig. 68.—Same egg as fig. 67, lateral view of A quadrant. 
Fig. 69. —Same egg as fig. 67, lateral view of B quadrant. 
Fig. 70.—Slightly later stage ‘than fig. 67, lateral view of C quadrant. 
Fig. 71.—Entomeres and mesomeres from egg of over 150 cells, seen from 
vegetative pole. 
Fig. 72.—Entomeres and mesomeres of egg about stage of fig. 71. 
Fig. 73.—Entomeres and mesomeres, seen from vegetative pole of egg slightly 
older than the two former stages. 
Fig. 74.— Vegetative pole view of about same stage as fig. 73, showing the 
overgrowth of the ‘“‘secondary’”’ mesoblasts (ecto-mesoblasts, 3a7""', 
3a"1l) 3b7""1, 3b*!!) by other cells of the third quartet. 
Fig. 75.—U pper pole view, about the same stage as fig. 74, showing trans- 
eee splitting of the arms of the cross and division of outer trocho- 
Dlasts. 
Pirate XXX, Fig. 76.—Upper pole view of somewhat later stage than fig. 75 
showing increase in breadth of cross area. 
Fig. 77.—Lateral view of stage similar to fig. 75, showing large excretory 
cell (8c!) and neighboring cells. 
Fig. 78.—Vegetative pole view of gastrula with closing blastopore, showing 
pointed anterior end and complete overgrowth of the ecto-mesoblast. 
Fig. 79.—Somewhat older gastrula than preceding figure. 
Fig. 80.—Optical section (parallel to ventral surface) of gastrula of about 
the stage shown in fig. 79. 
PLATE XXXI (except figs. 81-2), Figs. 81-84.—Optical sections, similar in direc- 
tion to that of fig. 80, through successively older gastrule, showing 
torsion of the enteron through increase in area of the left side (right 
