STUDIES ON THE PROTOOHOEDATA. 357 



EXPLANATION OF PLATES XXX & XXXI, 



Illustrating Mr. Arthur Willey's paper, " Studies on the 

 Protochordata.^' 



List of Reference Letters. 

 a. d. Adhering disc. a. g. Atrial groove, ant. b. c. Anterior body-cavity, 

 at. c. Atrial cavity, atp. Atriopore. br. Brain, br. c. Branchial cavity. 

 br. t. Branchial tract, cer. ves. Cerebral vesicle, cer. ves. res. Histolytic 

 residua of cerebral vesicle, cor. c. Coronal circlet at base of buccal tube. 

 ect. Ectoderm. e7id. Endostyle. h. Heart, hi/p. Hypophysis, int. Intes- 

 tine. /. m. Longitudinal muscle, m. Mouth, mes. b. Mesodermic band. 

 n. c. Nerve-cord. nch. Notochord, n. hy. p. Neuro-hypophysial pore. 

 n. hyp. c. Neuro-hypophysial canal, oes. (Esophagus, p. d. Posterior dila- 

 tation of nerve-cord, or " Rumpfganglion " of Kowalevsky. pc. Pericardium. 

 pc. g. Pericoronal groove, pr. I. Prgeoral lobe. py. g. Pyloric gland. 5^. 

 Stomach, st'.st". Stigmata, t. Remains of tale. #. i. Tongue-bar. t.b.v. 

 Transverse blood-vessel. /, //, III, IV. First four primary stigmata of 

 Ciena. 



PLATE XXX. 



All the figures on this plate relate to Ciona intestinalis. 



Fig. 1. — Left side of larva just before fixation. The anterior body-cavity 

 between the three adhering papillae and the endostyle, is filled with mesoderm. 

 At the base of the tail are also masses of mesoderm which are partly composed 

 of cells produced by transformation of the endodermic cells of the tail. In the 

 middle of the body the lumen of the branchial sac is reduced almost to nothing 

 by the pressure upon it of the large cerebral vesicle containing the eye and 

 otolith. Drawn from living object. Zeiss, 2, D. 



Fig, 2, — Right side of young Ciona just after fixation. The two apertures 

 which are present in the branchial tract are very indistinct at this stage, and 

 are represented by the two dark lines towards the centre of the branchial 

 tract. This is the most important stage for becoming acquainted with the 

 primary topographical relations of the various parts. Drawn from a prepara- 

 tion, Zeiss, 3, C. 



Fig, 3, — Left side of young Ciona in which the rotation of the body about 

 the prseoral lobe has commenced. The transition from the larval to the adult 

 condition of the nervous system will be fully discussed in a succeeding 

 " Study." From a preparation. Zeiss, 2, D. 



VOL. XXXIV, PART III. NEW SBR. A A 



