TUNICATES 169 



is, however, less sensitive, and its reactions are slower than in the 

 normal creature. 



A good accoiint of Tnuicates, their development and relation- 

 ships, is given by Arthur Willey in "Anipliioxus and the Ancestry 

 of the Vertebrates," 1SQ4, and also hy J. S. Kingsley in "The River- 

 side Natural History," Vol. III. Most valuable general treatises 

 upon the subject are also given Ijy W. Herdman in "Report on the 

 Tunicata," in the Reports of the Voyage of H. M. S. "Challenger," 

 Zoology, Vol. VI.; and by W. K. Brooks in "Salpa," Memoirs Jolms 

 Hopkins University Laboratory, 1893. A valuable summary for 

 Inglier students is given by W. A. Herdman in The Cambridge 

 Natural History, Vol. VII., pp. 33-138, Macmillan & Co., 190d. 



Ciona intestinalis (Fig. IISJ. This large sea-squirt is found 

 upon our shores, and is also abundant in the Mediterranean and on 

 the coast of England. It is found upon the under sides of stones or 

 upon the shady sides of wharf piles immediately below low tide level. 



It grows to be four inches long and the body is slender, and is 

 of the shape of an urn with two spouts, one at tlie narrow end and 

 one at a short distance below the terminal opening. The terminal 

 opening is at the forward end of the animal, and serves as a mouth 

 for the admission of water and food ; while the lower aperture arises 

 from the back of the creature and serves to carry off the water whicli 

 has passed through the numerous gill slits of the hiige throat, and 

 to conduct away the waste products of the body. 



The animal is dull yellowisli or greenisli in color, and the aper- 

 tures are bordered with brilliant greenish-yellow. The body is trans- 

 lucent, and there are from twelve to fourteen powerful strands of 

 longitudinal muscle fibres wliicli api^ear as opaque glistening lines. 

 If tlie animal be disturbed these longitudinal muscles contract rap- 

 idly, so that the creature shrinlis into a shape even broader than long. 



In common with all tunicates this creature is hermaphroditic 

 l3ut is practically incapable of fertilizing its own eggs. These are 

 discharged with clock-like regularity at one and one-half hours be- 

 fore sunrise by means of a series of violent contractions, and are 

 fertilized in the water by spermatozoa discharged from another 

 tunicate. The egg is covered with a membrane which rises into 

 papillfe, giving it the appearance of a chestnut bur made of glass 

 and with a few blunt spines. It develops into a little tadpole-shaped 



