33 
about half-a-minute ; it then beats in the opposite direction, thus 
constantly changing arteries to veins, and its veins to arteries. 
Small oval bodies can be seen in the body cavity ; these are the 
eggs. The young Phad/usta, when it has reached its full develop- 
ment within the egg, moves vigorously, causing the egg covering 
to burst. The little animal as it emerges from the egg has a 
notochord, above which lies a rudimentary medullary tube, and it 
then assumes quite a different form from that ofits parents. It has 
the same general characters as the young frog when in the tadpole 
stage. There is a slight difference in the shape of the mouth and 
position of the organs of vision,—the young Ascidian having but 
one eye, while the tadpole frog possesses two eyes, and, as Pro- 
fessor Ray Lankester has clearly shown, it had in common that 
which all other vertebrates had at one time of their lives, includ- 
ing man, a notochord, a throat perforated with gill-slits, a spinal 
cord, and a cerebral eye imbedded in its brain. 
In the spring of 1888 many of these animals were to be seen 
firmly fixed upon oyster shells, stones, and the walls of Tank No. 
26 in the Brighton Aquarium. I drew the attention of my 
fellow-student, Mr. J. E. Haselwood, M.R.M.S., to them, and, 
with the consent of the Aquarium Directors, Mr. Wells, the 
Superintendent, carefully removed some by sinking a jar to the 
bottom of the tank and then placing some oyster shells therein, 
without disturbing in the least the Ascidians attached to the 
shell. They were placed in a glass jar and regularly supplied 
with fresh sea-water, but after a few days they shrivelled up and 
died, much to our disappointment. 
Mr. Haselwood afterwards mounted some of the eggs, and 
they formed very interesting microscopic objects. We subse- 
quently visited the Royal College of Surgeons together, and, 
through the courtesy of Professor C. Stewart, were shown 
beautiful specimens of tadpole Ascidians in alcohol. 
At that early stage the young Ascidian swims about in the 
sea by means of its vertebrate tadpole-like tail, but this youthful 
condition is soon at an end. Then it sinks to the bottom of the 
sea, attaches itself by its head to stones, corals, shells, &c., and 
becomes permanently fixed. The tale atrophies, together with 
the notochord, and the body soon takes the shape of a leather 
bottle with two necks. 
We have, therefore, evidence that these lowly degenerate 
vertebrates were probably at a very remote period of the earth’s 
history the ancestors of all the great group of vertebrates, including 
man, and that one eye alone was the only organ of vision. The 
two eyes were afterwards developed. In the third non-functional 
parietal eye of the living New Zealand lizard, Sphenodon, we 
have doubtless a survival of the single cerebral eye of the retro- 
graded Ascidians, which form one of the most instructive 
