BUDDING PROCESSES OF CEPHALODISCUS DODECALOPHUS. 



527 



Plate IV. 



Fig. 60. Sagittal section through bud in fig. 26. 



Figs. 61-63. Transverse sections through bud in fig. 28. 



Figs. 64-68. Series of diagrammatic transverse sections through plumes and buccal shield at 

 various stages of development. 



Fig. 68a. Diagram of arrangement of tentacles and pre-oral lobe of Actinotrocha, but with the 

 tentacles projected forward as in Phoronis. 



Fig. 686. Diagram of the movement of a plume of Cephalodiscus from its point of origin to its 

 final position : ab. is the hypothetical path of the movement of the plume from the position in 

 Actinotrocha to that in Cephalodiscus, and cd. is a shortened path, the thick arrow showing the actual 

 path taken in the bud-development of Cephalodiscus. 



Figs. 69-74. Outline drawings illustrating the development of a plume and its pinnae. 



Figs. 75-77. Three stages of development of a single cell-element of the branchial eye. 



Figs. 78-84. Series of sections through the " sub-neural " region of bud with one pair of plumes. 

 (Zeiss. F.) 



Plate V. 



Fig. 85. Lateral view of Cephalodiscus with bud showing the principal nerve-tracts. 



Fig. 86. „ adult Cephalodiscus with peculiar cyst-like bodies in cloacal region. 



Figs. 87-89. Dorsal view of embryos in the egg-membrane, taken from the canals of the coencecium. 



Figs. 90-99. Series of transverse sections across the pharynx of Cephalodiscus (camera). 



Fig. 100. Diagrammatic drawing of the pharynx and connected structures of Cephalodiscus, 



LIST OF ABBEEVIATIONS. 



1.2.3. (in Plates I. and V.) = oral grooves. 

 1.2.3. (in Plate IV.) = plumes in order of develop- 

 ment. 

 c.c. = collar-cavities. 

 c.p. - collar-pores. 

 d.g. = dorsal groove. 

 d.s. = dorsal sinus. 

 g. =gut diverticulum. 

 gd. = gonaduct. 

 in. = intestine. 

 l.b.s. = lateral blood-sinus. 

 l.g. — lateral grooves. 

 l.m, = longitudinal muscles. 

 m.s. = median sinus. 

 m. = mouth. 



nc. =notochord (pleurochord). 

 ov. = ovary. 



p.c. = pharyngeal cleft. 



ph. = pharynx. 



p.l.l. = post-oral lamella. 



pn. = pinna, 



p.p. = proboscis pore. 



pr.coe. = pre-oral coelome. 



pr.s. = pre-oral sac. 



r. = rectum. 



sn.gl. = sub-neural gland. 



sn.s. = sub-neural sinus. 



st. = stomach. 



t.c. = trunk-cavity. 



v.g. = ventral groove. 



v.n. = ventral nerve. 



v.l.n. = ventrolateral nerve. 



v.s. = ventral sinus. 



VOL. XXXIX. PART III. (NO. 17). 



4 K 



