228 



THE ASCIDIANS. 



surface-view, but they are situated at the inner or con- 

 cave sides of the two thickenings. On either side of the 



latter can be seen the 

 ordinary cavity of the 

 pharynx proceeding to- 

 wards the oesophagus. 

 At a later stage the 

 openings of the two 

 first-formed stigmata 

 become distinctly visi- 

 ble (Fig. 105 C). Mean- 

 while a change of axis 

 is taking place in the 

 body of the young 

 Ascidian. 



During the extraor- 

 dinary change of axis 

 which we are about 

 to describe the probos- 

 ciform praeoral lobe 

 (snout, organ of fixa- 

 tion) remains station- 

 ary, and the rest of the 



Fig. 107. Young Ciona intestinal** after r j ar tiiallv rotates 

 the completion of the change of axis ; from the ' ! V 



left side. (After WILLEY.) through an angle of 90 



/, IV. Primary stigmata. a. Anus, situated , 



immediately below the left atrial aperture, end. degrees, USing the Or- 



Endostyle / Organ of fixation ^Ganglion f fixation as a 

 Ay. Hypophysis, int. Intestine, l.at. Left atrial 



aperture. /.;;/. Longitudinal muscle, m. Mouth, pivot about which it 



oes. (Esophagus. p.b. Peripharyngeal band. _. 



py. Pyloric gland, st. Stomach. /. Coronary turns. In Tig. IO5 6 



tentacles, v.n. Visceral nerve (cordon ganglion- tne rotation which 

 naire visceral). 



takes place very gradu- 

 ally is only half performed ; while in Fig. 107 it is complete. 

 The method of growth by which this rotation takes place 



