TUNICATES 169 
is, however, less sensitive, and its reactions are slower than in the 
normal creature. 
A good account of Tunicates, their development and relation- 
ships, is given by Arthur Willey in ““Amphioxus and the Ancestry 
of the Vertebrates,” 1894, and also by J.S. Kingsley in “The River- 
side Natural History,” Vol. III. Most valuable general treatises 
upon the subject are also given by 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 Johns 
Hopkins University Laboratory, 1895. A valuable summary for 
higher students is given by W. A. Herdman in The Cambridge 
Natural History, Vol. VIL, pp. 35-138, Macmillan & Co., 1904. 
Ciona intestinalis (Fig. 118). 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 the 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 which 
has passed through the numerous gill slits of the huge throat, and 
to conduct away the waste products of the body. 
The animal is dull yellowish or greenish 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 which appear as opaque glistening lines. 
If the animal be disturbed these longitudinal muscles contract rap- 
idly, so that the creature shrinks into a shape even broader than long. 
In common with all tunicates this creature is hermaphroditic 
but 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 
papilla, giving it the appearance of a chestnut bur made of glass 
and with afew blunt spines. It develops into a little tadpole-shaped 
