I 



castle: embeyology 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.i 



The season of spawning of Ciona probably extends in this country, as 

 in Europe, from spring to autumn. I 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 late 

 as the 2 2d 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 Xewport. 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 youthfuluess. 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 Tlie time of egg-laying is about the same — viz. just before daybreak — in the 

 case of Molgula Manhattensis,. on wiiich I made some observations in the United 

 States Fish Commission Laboratory at Wood's HoU, Mass., in June and July, 1894. 

 Cynthia, whose liabits 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 '93, Wiiley '94). Tiie manner ot 

 egg-laying is the same in Molgula as in Ciona. Herein my observations differ from 

 those of Kingsley ('83), 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 

 adliering 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 cap of very small micromeres resting on a few very large 

 macromeres. According 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. 



