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 wanning of the Atlantic palolo, 1898 to 1908. 



1 In 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 last 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, CeratocepJiale osawai, swarms 

 in the Tokyo River at the time of the /;<:' 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 sw r arm, 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 



