SENSORY STRUCTURES. 



403 



significance to the individual is uncertain ; perhaps it secretes some of 

 the mucus which entangles the food particles. 



Further, it is probable that all the following structures have some 

 sensory function, the pigment spots between the lobes of the apertures, 

 the tentacle-like processes beneath the mouth, and other processes 

 (languets) on the dorsal wall of the pharynx (absent in A. mentula]. 



Ex.ap. 



FIG. 128. Dissection of Ascidian. (After HERDM AN.) 



/.#/., Inhalant aperture; 7 1 ., tunic, cut away below to show 

 muscular layer, pharynx, &c. ; En. t endostyle or ventral groove of 

 pharynx. Note removal of pharynx to show, on the other the left 

 side, stomach (St.\ intestine (with fold seen at incision), and repro- 

 ductive organs (G.) ', H., heart; G.D., genital duct; A., anus; 

 C7., cloacal chamber ; Ex.ap., exhalent aperture; Gn., lies above 

 the ganglion which is seen between the two apertures. 



