270 GILBERT C. BOURNK. 



EXPLANATION OF PLATES 19—23, 



Illustrating Dr. G. C. Bourne's paper on "Oligotrema 

 psammites, a new Ascidiau belonging to the family 

 Molgulida3." 



Lettering in all the Figures. 

 amc. Amcebocytes. an. Anus. cfrw. Tentacular arm. arm'. Muscular core 

 of tentacular arms. At. Atrium. At. o. Atrial aperture. At. si. Atrial 

 siphon, bl. Blood-space. Br. Branchial aperture. Br. s. Branchial sac. 

 Br. si. Branchial siphon, d.sus. Dorsal suspensory fold. dt. Dorsal tubercle. 

 ecp. Ectoplerome. etip. Endoplerome. ect. Ectoderm, ect. i. Ectoderniic 

 ingrowth. e,v. c. Excurrent chamber, gl. Subneural gland, (/r. Yellow 

 granules in ectoderm. Hi. Heart, ic. Incurrent chamber, int. Intestine. 

 /. mus. Longitudinal muscles. L.od. Left oviduct. L.pbc. Leff. peribranchial 

 cavity. L. spd. Left sperm-duct. M. Mouth, nms. Muscle-bands, mus. 

 dil. Dilator muscle of branchial siphon, mus. ext. Extensor muscles of arm. 

 mus. flex. Flexor muscle of arm. N. Nerve-ganglion, n. Nerve, Oe. (Eso- 

 phagus. OS. g. (Esophageal groove. Ov. Ovary. Od. Oviduct, pin. Pinna; 

 of arms, fl, Plerome. fhr. Cavity of prebranchial zone. R. Renal organ. 

 H. od. Bight oviduct. R. pbc. Bight peribranchial cavity. R. spd. llight 

 sperm-duct. Sph. Sphincter muscle. St. Stomach. St'. Distal limb of 

 stomach, s. s. Stigmata. T. Test. tn. Oral tentacles. Tt. Testis, vp. 

 Vascular processes, v. sus. Ventral suspensory fold. x. Cavity (? artificial) 

 lined by ectoderm, y. Bristle passed into the 11. peribranchial cavity in fig. 31. 



PLATE 19. 



Fig. 1. — An enlarged drawing of 0. ])sam mites seen from the left side. 

 The actual size of the animal is imlicated by the line on the left of the figure. 



Fig. 2. — An enlarged drawing of the oral aspect of 0. psammites, show- 

 ing the transversely elongated branchial aperture surrounded by six pinnate 

 arms. 



Fig. 3. — A view of the principal organs in situ, as seen through the trans- 

 ])arent body-wall, after the test has been opened by a longitudinal cut. 



Fig. 4. — A view of the branchial sphincter muscle and the six tentacular 

 arms from below. 



Fig. 5. — One of the muscular arms removed from the test, showing the 

 arrangement of the muscles. 



Fig. G. — A section (somewhat oblique) through the branchial siphon and the 

 bases of three of the tentacular arms. 



