THE EXOGONE.E. 24") 



Fig. 52. Stage in the epiboly in which the four original cells (inacromeres) still maintain 

 their individuality : the nuclei of these are marked with small crosses, x 440. 

 •33. Lateral view of embryo with dorsal plate and stomodoeal rudiment, before the 

 appearance of the germinal bands. 



54. Lateral view of an embryo at a somewhat later stage than that represented in 



fig. 53, with the pair of narrow bands running from the stoniodreal rudiment to 

 the apical plate. 



55. Ventral view of an embryo of about the same stage as that represented in fig. 54, 



but with the stomodceal rudiment more extended laterally and the germinal 

 bands beginning to appear. 



56. Lateral view of a similar stage to that represented in fig. 55. 



57. Lateral view of a somewhat more advanced stage with the dorsal plate extending 



forwards nearly to the free end. 



All the figures, except 67 and 68, refer to Exogoiiefustifera. 



Fig. 58. Ventral view of an embryo at the stage in which the germinal bands meet 

 posteriorly : the stomodaaal rudiment, transversely elongated and connected with 

 the dorsal shield by a pair of narrow strands, is not vet definitely invaginated. 

 X440. 



59. Transverse section of embryo at about the stage represented in fia;. 58. x 440. 



so. here points to the germinal band. 



60. Ventral view of an embryo with the stomodteal invagination completed, the 



germinal bands well established, meeting behind to surround a proctoda?al area. 

 X 440. 



61. Lateral view of the embryo represented in fig. 60. x 440. 



62. Ventral view of embryo in which the germinal bands have become segmented and 



the stomodasum, destined to become the pharynx, has given off an offset which 

 will develop into the proventriculus. X 440. 



63. Horizontal section of stage similar to that represented in fig. 62. X 1000. 



64. Stage of the first appearance of the tentacles, x 440. 



65. Stage with well developed prostomial tentacles and without rudiments of the 



parapodia. x 440. 



66. Horizontal section of advanced embryo with fiv 3 segimnts and parapodia with 



seta;, x 440. 



67. Grubea Iterguelensis. Stained and cleared early embryo, viewed somewhat obliquely 



from the ventral side. The dorsal plate deeply constricted into head plate and 

 body plate, and the latter giving off ventrally the germinal bands, x 440. 



68. Grubea quadrioculata. Late embryo stained and cleared : outline, to show the 



ventral curvature. X 300. 



LINN. JOrEN. — ZOOLOGY, VOL. XXXIV. 19 



