1904.] NATURAL SCIENCES OF PHILADELPHIA. 405 



of figures). Fig. S4 represents a section taken tlirough a young 



veliger about the stage of tliat shown in fig. 104. 

 Fig. So. — Actual section through a gastrula similar in age to fig. 80 and in 



same plane. 

 Fig. S6. — Actual section (sagittal) through a gastrula about the age shown 



in fig. 95. 

 Fig. 87. — Actual section (about 30° to the right of the sagittal plane) 



through a young veliger slightly older than as shown in fig. 104. 



Plate XXXTI {except -fig. 94), Figs. 88-89.— Actual sections (nearly horizon- 

 tal) througli a veliger about the stage shown in fig. 105, showing 

 cerebral and pedal ganglia, pedal commissure and otocysts; also large 

 excretory cell on right side of larva and large enteric cell on same 

 side of enteron. 



Figs. 90-93. — Four successive horizontal actual sections through a veliger 

 slightly older than that shown in fig. 107. 



Fig. 94. — Nearly horizontal actual section through veliger of same age as 

 preceding series, showing nerve ring around oesophagus. On PI. 

 XXXI. 



Plate XXXIII, Fig. 95. — Gastrula, seen from right side, showing first indica- 

 tion of the first velar row (V'). 



Figs. 96-97. — Upper and lower sides respectively of gastrula of the same 

 age as shown in fig. 95. 



Figs. 98-99. — Lateral (right) and lower sides of a veliger slightly older than 

 that shown in figs. 96-97. 



Fig. 100. — Left side of gastrula somewhat older than that shown in the two 

 preceding figures. 



Plate XXXIV, Figs. 101-102.— Anterior and right-lateral views of larva mid- 

 way between gastral and veliger stages. The deep invagination of 

 the shell-gland (Sh.G.) has formed and the stomodseal pit (St.) is 

 well marked. 



Figs. 103-104. — Anterior and right-lateral views of a young veliger. The 

 shell-gland has opened outward, the foot (Ft.) is becoming evident 

 and the velar lobes are just beginning to appear. 



Fig. 105. — Veliger, seen from right side, somewhat older than the preceding 

 one, showing further development of velar lobes and foot, developing 

 shell, differentiation of enteron and larval musculature. 



Fig. 106. — Slightly older veliger than fig. 105, seen from right side. 



Plate XXXV, Figs. 107-108. — Dorsal and anterior views of the same veliger 

 somewhat older than fig. 106. The shell and the velar lobes show 

 considerable advance in development. 

 Figs. 109-110. — Right-lateral and dorsal views of the same veliger just 

 before hatching. The dotted lines represent the probable shape of 

 the posterior vesicle before shrinkage. 



