LIST OF REFERENCE-LETTERS. 



a. arm. 



17. h. arm-base. 



al. alimentary canal. 



au. anus. 



a. V. anterior vessel of stalk. 



a. V.' anterior vessel of body. 

 /;. bud. 



b. c.' proboscis-cavity. 

 b. €.''■ collar-cavity. 



b. c} a. anterior dorsal hom of collar-cavity. 

 b. c.'^ metasomatic cavity. 



b.c? a. anterior ventral horn of metasomatic cavity. 

 b. c.^ b. part of metasomatic cavity in loop of aliment- 

 ary canal. 

 b. /■«. basement-membrane. 



b. ït'. body-wall. 



c. coUar. 



c. c. collar-canal. 



c. c. e. external opening of collar-canal. 



c. c. i. internal opening of collar-canal. 



c. n. s. central nervous system. 



d. basal disc of stalk. 



div. dorsal diverticulum of pharynx. 



d. ui} dorsal mesentery of collar. 



d. 111? dorsal mesentery of metasome. 



d. V. dorsal vessel. 



e. embryo. 

 ep. epidermis. 



e. r. epithelial ridge. 

 exc. excretory granules. 

 ƒ. fold of body-wall. 



f. c. food-channel. 



f. c. l. left food-channel. 

 /. c. r. right food-channel. 

 fil. peristomial filament. 



g. gonad. 



gl. glomerulus. 



g- p- generative pore. 



g.s. gill-slit. 



g. s. £. external opening of gill-slit. 



int. intestine. 



L. I — 6. left arms. 



L. a. left arm. 



I. g. labial or oral groove. 

 /. n. lateral nerve. 



;;/. mouth. 



vies.^ dorsal mesentery of collar. 



rnes.^ dorsal mesentery of metasome. 



met. metasome or trunk. 



m. r. mid-rib of peristome. 



ms. longitudinal muscles of metasome. 



ms.p. muscles of proboscis. 



ncJi. notochord. 



II. t. nerve-tract. 



o. orifice of coenoecium. 



ocs. oesophagus. 



op. operculum. 



op. l. left lobe of operculum. 



op. r. right lobe of operculum. 



op. ree. recess at base of operculum. 



or. 111. oral muscle (of collar). 



or. s. oral sinus (?). 



ov. ovary. 



ovd. oviduct. 



ov. l. left ovary. 



ov. 111. ovarian mesentery. 



01'. r. right ovary. 



01'. V. ovarian vessel. 



/. proboscis. 



/.' its ventral lobe. 



p. b. pigment-band of proboscis. 



per. pericardium. 



per. s. pericardial sinus or heart. 



pil. pharynx. 



pi. g. plcurochordal groove. 



post.p. posterior pit of embryo. 



