06 EVENINGS AT THE MICROSCOPE. 



wide gullet, into an oblong stomach, the lower portion of 

 which is obtuse. An extremely attenuated duct connects 

 this, which is probably the true stomach, with a globular, 

 rather small, intestine, which is again connected by a 

 lengthened thread with the base of the cell. By an 

 arrangement common to the ascidian * type of the diges- 

 tive function, the food is returned from the intestine into 

 the true stomach, whence the useless parts are discharged 

 through a wide and thick tube that issues from it close 

 behind the point where the gullet enters. This tube 

 passes upwards parallel to the gullet, and terminates by an 

 orifice outside and behind the base of the tentacles. All 

 these viscera are beautifully distinct and easily identified, 

 owing to the perfect transparency of the walls of the cell, 

 the simplicity of the parts, and their density and dark 

 yellow colour. All of them are manifestly granular in 

 texture, except the slender corrugated tube which connects 

 the stomach with the globose intestine : this is thin and 

 membranous, and is doubtless, if I may judge from analogy, 

 capable of wide expansion for the passage of the food-pellet. 

 The sudden contraction of the polypide into its cell 

 upon disturbance or alarm, and its slow and gradual 

 emergence again, afford excellent opportunities for study- 

 ing the forms, proportions, and relative positions of the 

 internal organs. In contraction, the globular intestine 

 remains nearly where it was, but the stomach slides down 

 into the cell behind it, as far as the flexible duct will 

 allow, and the thick gullet bows out in front, showing 

 more clearly the separation between it and the rectum, 

 and the insertion of both into the stomach. This retrac- 

 tion is, in part, effected by a pair of longitudinal muscular 

 bands, which are inserted at the back of the bottom part 

 of the cell, and into the skin of the neck below the ten- 



* The Ascidia are a low order of animals growing in masses in the 

 sea, with bodies like little leathern pouches ; whence their name, from 

 a Greek word aoxbs (askos), meaning pouch. 



