CASTLE: EMBRYOLOGY OF CIONA INTESTINALIS. 211 
of the atrium simultaneously with the release of the sexual products 
from their respective ducts, must secure under natural conditions a 
wider distribution and more thorough mixing of the eggs and sperma- 
tozoa than would otherwise occur.! 
The season of spawning of Ciona probably extends in this country, as 
in Europe, from spring to autumn. have never collected adult speci- 
mens which did not contain mature eggs and spermatozoa, though I 
have taken them as early in the season as the 10th of June and as lato 
as the 22d of September. 
The development of the ovum is very rapid, as I shall show further 
on, and the larval period brief. The growth of the metamorphosed 
individual must also be very rapid, as the following facts indicate. In the 
summer of 1892 specimens of Ciona were abundant in a certain locality 
at Newport. But the succeeding winter was a cold one, and seems to 
have killed off those individuals which were situated in very shallow 
water. In the summer of 1893 specimens were to be found only at a 
depth of over two feet below low-water mark. In August and Septem- 
ber of the next year, however, they occurred in abundance just below 
low-water mark. But those so situated were rather small, not exceed- 
ing 7 cm. in length, very clear, and free from dirt or parasitic growths, 
thus giving evident signs of youthfulness. They cannot have been over 
fifteen months old, and may have been much younger. Yet they were 
sexually mature, and produced eggs in abundance. 
1 The time of egg-laying is about the same — viz. just before daybreak — in the 
case of Molgula Manhattensis, on which I made some observations in the United 
States Fish Commission Laboratory at Wood's Holl, Mass., in June and July, 1894. 
Cynthia, whose habits I studied at the same place, lays its eggs with equal clock- 
like regularity, but toward nightfall instead of at daybreak. The late afternoon is 
also the time of spawning for Amphioxus (Wilson ’98, Willey ’94). The manner of 
egg-laying is the same in Molgula as in Ciona. . Herein my observations differ from 
those of Kingsley (89), who states that in Molgula fertilization occurs within the 
atrium, and that the eggs are for some time afterward retained there. I have 
never found embryos within the atrial chamber, though I have often seen them 
adhering to the bodies of the parent individuals, where some eggs had probably 
settled at the time of spawning. My observations regarding the manner of 
cleavage in M. Manhattensis also differ from those of Professor Kingsley. He 
states that the cleavage is unequal, much as in certain Mollusks, and results in 
the formation of a eap of very small mieromeres resting on a few very large 
maeromeres.  Aceording to repeated observations of my own, made both on 
naturally and on artificially fertilized eggs, the cleavage progresses very much 
as in other Ascidians, the first two cleavages being equal. I think Professor 
Kingsley must have been misled by appearances in immature eggs obtained by 
dissecting out the ovaries for artificial fertilization. 
