1882.] 
445 
[Kingsley. 
time of hatching to that of attachment varies considerably ; some 
specimens affixed themselves to the glass in which they were 
reared in less than a day while others pursued a life of freedom 
for three or four days. I did not closely follow the method in 
which the notochord breaks down, but soon after hatching (fig. 11) 
all of the segmented character of the tail is lost, and soon one 
finds in the degenerated notochord large numbers of vacuoles, 
which have a slight pinkish hue, forming a pleasing contrast with 
the prevailing yellow of the embryo. With the hatching the 
tail is constricted at its junction with the body in the same man- 
ner as if it were to drop off, but this does not occur. At 2 
p. m. of June 6th I made the drawing (fig. 11), and about half 
an hour later the vacuoles (fig. 12) made their appearance. The 
specimen was then set aside, and when next examined, at 5 p. m., 
fig. 13 wrns drawn from the same specimen, the changes which 
occurred in three hours were very marked and though watched 
step by step in subsequent specimens a simple description of the 
drawings will cover the ground. The tail has shrunken to about 
half of its former length, the vacuoles have disappeared and the 
organ has greatly increased in diameter, a consequence of its 
shortening. Wrinkling of the margins of the tail are also visible. 
This shortening of the tail brings into view the sheath in which it 
was enveloped, only a portion of which is shown in the figure. 
This sheath is seen to envelope the entire length of the tail and 
on the contraction of the fleshy portion longitudinal plications 
are formed in the distal portions. It was this folding of the 
caudal sheath and the wrinkles in the body of the tail which 
Professor Morse 1 has mentioned as fin rays. The central line of 
bodies which he has compared with vertebrae are simply the 
contracted central portions of the tail, and any attempt to 
use the evidence presented by his paper as grounds for the Ver- 
tebrate character of the Ascidians is impossible. The caudal 
sheath under the highest power to which I had access (a one-fif- 
teenth immersion of W ales 2 ) showed no traces of structure. It per- 
sists for a considerable while and disappears by a gradual disinte- 
iProc. Bost. Nat. Hist., xiv, 351. 
2 For the use of this lens and for many other facilities I am indebted to the kindness 
of Prof. Alpheus Hyatt. . 
