ANATOMY AND DEVELOPMENT. 235 



condition. Out of the multitude of stigmata which are 

 present in the adult Ciona only four arise by independent 

 perforation ; namely, the primary stigmata I. and IV. 

 (which we regard as the two halves of a primitively single 

 slit) and V. and VI. 



First Appearance of Musculature. 



By the time the change of axis of the entire body of 

 the young Ciona has been effected the musculature 

 characteristic of the adult begins to put in an appear- 

 ance. In Fig. 107 circular sphincter muscles are present 

 round the buccal and atrial apertures. The latter are still 

 paired, but are carried by differential growth dorsalwards 

 at a later stage, and finally coalesce together in the dorsal 

 middle line to produce the single atrial aperture of the 

 adult. 



One strand of the longitudinal muscles of the later 

 muscular mantle is likewise to be seen in Fig. 107. It 

 tends to branch dichotomously. Posteriorly it is inserted 

 on the inner surface of the organ of fixation near the point 

 where it joins on to the body. Later new muscle-bands 

 arise similar to the first, and become distributed over the 

 body-wall in a spreading fan-like fashion, but posteriorly 

 they are all inserted in the same region of the organ of 

 fixation. 



Alimentary Canal and Pyloric Gland. 



The course of the alimentary canal can be gathered so 

 plainly from the accompanying figures (Figs. 105 and 107) 

 that it hardly needs a verbal description. From the 

 posterior dorsal corner of the branchial sac the oesophagus 

 leads into the wide stomach, and from the latter, again, 

 the intestine, which often possesses a strangulated appear- 



