1902.] CONKLIN— EMBRYOLOGY OF A BRACHIOPOD. 75 



Fig. 30. Dorsal view of a larva of the same stage as the preceding, showing the 

 dorsal mantle fold {Md); the anterior and posterior mantle furrows; the 

 union between the two halves of the peduncular ccelom. 



Plate VI. 



Fig. 31. Lateral view of a larva of the same stage as the preceding, showing 



anterior and posterior mantle folds {Fa and Fp)^ apical and ventral sense 



plates ( CG and SG), enteron and ccelom. 

 Fig. 32. Dorsal view of older larva, showing increased prominence of mantle 



and deep constriction of anterior mantle furrow. 

 Fig' ZZ' I^orsal view of an older larva, showing the mantle in process of 



growing back over the peduncle ; the ccelom is almost entirely confined to 



the mantle. 

 Fig. 34. Dorsal view of one of the oldest free-swimming larvae ; the mantle has 



almost entirely covered the peduncle. 

 Fig. 35. Lateral view of a larva of the same stage as the preceding, showing 



apical and ventral sense plates ( CG and SG), dorso-ventral extension of 



enteron and greater width of mantle chamber on dorsal side. 

 Fig. 36. Optical section in longitudinal frontal plane of a larva of the same 



stage as the preceding, showing apical sense plate and cerebral ganglion ; 



mantle chamber and setae sacs ; cephalic, peduncular and mantle ccelom 



[Cc, Cp, Cf?i). 



Plate VII. 



Fig. 37. Section of an embryo of the stage shown in Fig. 13, showing dark 



staining granules in the outer ends of the cells and yolk spherules in the 



blastocoel. 

 Fig. 38. Section of an embryo of the stage shown in Fig. 14. 

 Figs. 39-42. Four transverse sections of an eaabryo of the stage shown in Fig. 



20 ; Fig. 39 being the most posterior and Fig. 42 the most anterior section 



drawn. 

 Figs. 42r7 and 42^. Longitudinal sections through an embryo of about the same 



stage as is shown in Figs. 39-42, showing the formation of the septum which 



separates the enteron from the enterocoel. 



Plate VIII. 



Figs. 43-47. Five transverse sections of a larva of the stage shown in Fig. 



24; Fig. 43 being the most anterior and Fig. 47 the most posterior section 



drawn. 

 Figs. 48-52. Five transverse sections of a larva of the stage shown in Fig. 



29; Fig. 48 being the most anterior and Fig. 52 the most posterior section 



drawn. 



