358 AETHUK WILLEY. 



Fig. 4. — Right side of young Ciena of same age as preceding. At py. g. and 

 int. are seen the openings of the pyloric gland and intestine into the stomach. 

 Preparation. Zeiss, 2, D. 



Fig. 5. — Left side of young Ciona in which the change of axis is com- 

 pleted. A small intermediate slit is being constricted off from IF. The 

 branching of the pyloric gland should be noted. From a preparation. Zeiss, 

 2, C. 



Figs. 6 — 10. — Different stages in the formation of the intermediate stig- 

 mata // and III. All from living object. 



Fig. 6. — Stigmata of left side before the appearance of the intermediate 



stigmata. Zeiss, 4, B. 

 Fig. 7. — Ventral extremities (i. e. nearest endostyle) of stigmata of left 

 side at a slightly later stage than preceding. The two stigmata are 

 in connection with one another. Zeiss, 4, D. 

 Fig. 8. — Similar view to preceding at still later stage. Zeiss, 3, C. 

 Fig. 9. — Stigmata of right side at the stage of the actual formation of 

 the intermediate stigmata. Ill has already become independent, while 

 II is still a part of I. Zeiss, 4, B. 

 Fig. 10. — Stigmata of left side of same individual as preceding. Same 

 magnification. 

 Figs. 11 and 12. — Oblique transverse sections through branchial sac of 

 young Ciona of the stage shown in Fig. 2 to show the primary relations of 

 the two first-formed branchial apertures. In Fig. 12 the atrial aperture is 

 cut tangentially. In the same Fig. the pericardium is included in the section 

 where it is seen to lie to the left of the middle line in the section, that is, on 

 the right side of the body of the larva. Zeiss, 3, D. 



Fig. 13. — Horizontal section through young Ciona of the stage of Figs. 3 

 and 4. The section only passes through the actual atriopore on the right side 

 (left of the section). On the other side the atriopore is cut tangentially, as 

 also is the branchial aperture {IV) on each side. The section is slightly 

 oblique, and is of value from a topographical point of view. Zeiss, 3, D. 



Fig. 14. — Stigmata of left side showing the addition by fresh perforation 

 of No. 5. Zeiss, 4, B. 



Fig. 15. — Transverse section through the prseoral region of a tadpole of 

 Ciona of the stage represented in Fig. 1. The endostyle is cut vertically 

 and longitudinally, since its long axis at this and the next stage is dorso- 

 ventral. Zeiss, 3, E. 



Fig. 16. — An abnormal case in which the primary stigmata (I and IV of the 

 left side) had fused together at their ventral ends, i. e. the ends towards the 

 endostyle. The two stigmata of the right side of this individual were inde- 

 pendent of one another. From living object. Zeiss, 3, C. 



