STUDIES ON THE PEOTOOHOBDATA. 359 



PLATE XXXI. 



Fig. 17. — Secondary stigmata of the right side of young Ciona illustrating 

 their production by subdivision of the primary stigmata. From living object. 

 Zeiss, 2. B. 



Fig. 18. — One transverse row of secondary stigmata at a later stage than 

 preceding to illustrate their change of axis. From living object. 



Fig. 19. — Ventral view of stomach, intestine, and pyloric gland, in optical 

 section, at a stage intermediate between Figs. 2 and 3, to show that the 

 primary nature of the pyloric gland is that of a csecal diverticulum of the 

 pyloric region of the stomach. Zeiss, 3, D. 



Figs. 20 — 24 and Fig. 30 relate to Ciona intestinalis, and are all drawn 

 from living object, and Figs. 25 — 29 to Clavelina lepadiformis. 



Fig. 20. — Stigmata of right side in an abnormal specimen in which II and 

 ///had fused together and were represented by one peculiarly shaped aper- 

 ture. Between / and IV are also shown two papillae {x,y) which project into 

 the branchial cavity, and from which the formation of the longitudinal and 

 transverse blood-vessels proceeds. Zeiss, 3, C. 



Fig. 21. — Stigmata of left side of a young Ciona showing addition by fresh 

 perforation of No. 6. Zeiss, 4, B, 



Fig. 22. — Portion of two transverse rows from the branchial sac of a young 

 adult Ciona with eleven rows of stigmata, showing the origin of the succes- 

 sive transverse rows by subdivision from pre-existing rows, and not by fresh 

 perforations. Zeiss, 2, C. 



Figs. 23 and 24. — Two stigmata from the branchial sac of same individual 

 as preceding, exhibiting unequal division. In Fig. 24, when the constriction 

 at the lower end of the slit is completed, the resulting smaller aperture might 

 be thought to have arisen by fresh perforation, but it does not do so, as the 

 figure shows. Zeiss, 2, C. 



Fig. 25. — Transverse section through branchial region of a very early 

 larva of Clavelina before the appearance of the atrial involutions or of 

 pigment in the brain, and while the neuroporus is still present, to show first 

 origin of pericardium. Zeiss, 2, D. 



Figs. 26 and 27. — Transverse sections through a rather older larva of 

 Clavelina, to show the atrial grooves, pericardium, and body-cavity, as com- 

 pared with Fig. 25. Fig. 26 passes through the first rudiment of the eye in 

 the brain, and Fig. 27 passes through the so-called post- vesicular ganglion, 

 in which the ventral wall of the neural canal is much thickened. Zeiss, 2, D. 



Fig. 28. — Bather oblique transverse section through a still older larva of 

 Clavelina, showing on the left side (right of the section) the opening of the 

 neuro-hypophysial canal into the branchial sac, and on the other side the 



