The Annual Breeding-Swarm of the Atlantic Palolo. 109 
quarter. The following record gives the date of the principal swarm in 
heavy type, while the dates upon which only a few worms were observed 
swarming are shown in ordinary type. 
Record of the swarming of the Atlantic palolo, 1808 to 1908. 
| _ Dates upon which | Date of moon’s | Dates u hich Atlantic Date of ‘ 
t pon whic tlantic | ate of moons | 
| Year. Atlantic palolo last quarter. — palolo swarmed. last quarter. 
| swarmed, 
ee 4 eee | z tlhe at 2a 
| 1898 | July 9, t0......... July 10 Ups My PgkS cnc eae artes akan | July 17 
| 1899 De 2k. ceesceee June 29 1905 OQ LOW 2h pe 23024 es | 24 
11900 lt demenepeoeer July 18 1906 A Ts ee 13 
1902 | 24, 25, 28... 2 |, 190 DL Ja acedecesecmanpedonocn | 2 
| 
1008 NO 1G). 3 dnsccreoetss caus 19 
1In 1900 and 1903, the dates of the principal swarm were observed by Mr. George R. Billbury, 
and I know nothing of the less conspicuous swarms of those years. In other years the swarms were 
observed by the author. No observations were made in 1901 and 1904. 
The most interesting fact revealed by the above table is that in 1905, 
when the last quarter of the moon came late in July, about 200 worms 
were observed swarming on July 9, and a few fresh-laid eggs were found 
on the morning of July 10. The first quarter of the moon fell on July 9, 
1905, and it is evident that the worm may respond to the first as well as 
to the /ast quarter of the moon. In 1908 the maximum swarm came on 
July 10, and the first quarter fell on July 6. A fair swarm also came on 
July 19, the day of the moon’s last quarter; and these were the only swarms 
of the year. This is the more interesting in view of the observations of 
Osawa and Izuka that the Japanese palolo, Ceratocephale osawat, swarms 
in the Tokyo River at the time of the new and the full moon. 
For the past five years I have been carrying out experiments designed to 
determine the nature of the stimulus to which the Atlantic palolo responds 
when it swarms. If at any time before the date of the normal swarm we crack 
open the rock within which a full-grown worm is living, the mechanical 
shock will often cause the worm to crawl partially or wholly backward 
out of its burrow. The worm is then very apt to break itself into lengths, 
and the sexual end often swims through the water with the corkscrew 
movement characteristic of the normal swarm. The worm may even con- 
strict its muscles and cast out its genital products; but this is never done 
with such completeness as in the normal swarm, and even if the eggs be 
cast out within 24 hours of the date of normal swarm, they do not mature 
and no embryos develop. 
Any appreciable impurity in the water, or the lack of sufficient circula- 
tion, will prevent the worms from swarming at the normal time. If we are 
to obtain reliable results, the water in which the worms are living must be 
free from an excess of carbon dioxide or other products of putrefaction, and 
this fact renders the experiments difficult of execution. In partially stag- 
nant water the worms may live very well, but they will not take part in the 
