REFERENCE LETTERS FOR FIGURES. 



a aim.-. 



a. c. i- adult collar cavity (Ikeda). 



at', v afferent blood vessel. 



al. c alimentary canal. 



a. p anal papilla. 



art artefact. 



a. t adult tentacle. 



a. t. m transverse septum of adult. 



b. c blood corpuscles. 



1). c. m blood corpuscle masses. 



b. t basement tissue ( Benham). 



ca? blood caecum. 



c. c collar cavity. 



eg ciliated groove ( Andrews i. 



c. \v collar wall. 



d. a digestive area. 



d. in. t dorsal muscle tract. 



d. v dorsal vessel ( afferent ). 



d. ve distributing vessel. 



ef. v efferent vessel. 



eg egg. 



e. b edge of hood. 



ep epistome. 



ex. c excretory cell. 



H flagellum. 



g ganglion. 



g. c ganglion cell. 



g. m. c giant mesoderm cell. 



in. c infraseptal cavity. 



int intestine. 



lat. n lateral nerve. 



1. 1. c left lateral cavity. 



1. 1. m left lateral mesentery. 



1. 1. n lateral longitudinal nerve. 



1. in longitudinal muscle. 



1. r. m ring muscle tract of lobe. 



1. r. n ring nerve tract of lobe. 



1. t larval tentacle. 



m mesoderm. 



in. 1 mesentery between preoral 



lobe and collar cavities. 



m. 2 mesentery between collar 



and trunk cavities. 



m. c. m mesodermal cell mass giv- 

 ing rise to blood corpus- 

 cles. 



in. f muscle fiber. 



m. 1. n median longitudinal nerve. 



m. s mesodermal sac of preoral 



lobe. 



n. c nepliridial canal. 



neph nephridium. 



EXPLANATION 



neph. o nepliridial opening. 



n. f nerve fiber. 



n. f. 1 nepliridial funnel into rec- 

 tal body cavity. 



n. f.- nepliridial funnel into lat- 

 eral body cavity. 



n. p nepliridial pit. 



nu nuclei of ciliated cells of 



perianal ring. 



ces. m oesophageal mesentery. 



p. an. s perianal space. 



pig pigment. 



p. o. c preoral body cavity. 



p. o. 1 preoral lobe. 



p. r perianal ring. 



p. re posterior recess I Ikeda). 



subneural sinus (Master- 

 man ). 



r rectum. 



r. b. v ring blood vessel. 



r. c rectal cavity. 



r. d. in rudimentary dorsal mesen- 

 tery. 



ret retractor muscle. 



r. 1. c right lateral cavity. 



r. in rectal mesentery. 



r. n ring nerve. 



r. ve recipient vessel. 



sen. p sensory papilla. 



sp. in sphincter muscle. 



st stomach. 



sup. c supraseptal cavity. 



t tentacle. 



t. b. v tentacular blood vessel. 



t. c trunk cavity. 



th ventral thickening of ecto- 

 derm. 



t. in. t tentacular ring muscle tract. 



t. n. t tentacular ring nerve tract. 



t. r tentacular ridge. 



v vestibule. 



ves glandular vesicles in ecto- 

 derm. 



v. in ventral mesentery. 



v. in. t ventral muscle tiact. 



v. n. t ventral nerve tra;t. 



v. p ventral pouch. 



v. p. ventral pouch opening. 



v. v ventral blood vessel (effer- 

 ent i. 



v. w. h ventral wall of hood. 



OF FIGURES. 



The objectives used in this work are the jj and J Spencer and the ,'_. Zeiss Oil Immersion. The occulares used 

 are the " X4" and " X 8 " Spencer and the No. 12 Zeiss Compensating. 



113 



