354 ON THE DEVELOPMENT OF THE PECTINIBRANCHIATA. 



Fig. 26. An embryo, strongly attached to the mass, x 100. a, membrane; 



b, foot; c, ova, grouped in various stages. 



Fig. 27. Embryo, x 100. a, membrane, ciliated here and there; b, foot; 



c, peduncle ; d, rudimentary lobe ; e, grouped ova. 



Fig. 28. Embryo, X 100. a, membrane ; b, foot ; c, lobe ; c?, exuded mass; 



e, grouped ova. 

 Fig. 29. Embryo, X 100. o, shell ; b, mantle ; c, foot ; d, lobe ; e, auditory 



organ ; /, grouped ova. 

 Fig. 30. Embryo, viewed laterally, x 100. a, shell; 6, mantle; c, grouped 



ova; d, foot ; e, lobe ; /, auditory organ ; g, salivary gland ; h, heart ; 



z, rudimentary stomach. 

 Fig. 31. Embryo, viewed laterally, x 100. a, b, c, d, e,f, g, h, as in fig. 30; 



i, proboscis ; k, oasophagus ; /, tentacle ; m, eyes ; n, cerebroid ganglia. 

 Fig. 32. Embryo, viewed laterally, X 100. Letters as before, except /, sto- 

 mach ; m, intestine ; n, anus ; o, tentacles ; p, eyes ; q, cerebroid 



ganglia ; r, commissure ; s, pedal ganglia. 



Plate XII. 



Fig. 1. Heart, x about 450. a, auricle; b, ventricle; c, primitive muscular 



tubes; d, large vessel. 

 Fig. 2. Calcareous network, x about 450. 

 Fig. 3. Embryo at the twenty-third day. 

 Fig. 4. Salivary gland. 

 Figs. 5, 6, 7, 9. Embryos further advanced. 

 Fig. 8. Developing branchia. 



THE EXD. 



