2 bulletin: museum of compaeative zoology. 



We will first present an accouut of the swarming of the Atlantic 

 Palolo, and will then give a description of the adult worm, a history of 

 the development of its larva, and finally some general conclusions con- 

 cerning the breeding habits of Polychsetse. 



It seems probable that the time of the swarming of the Atlantic 

 Palolo is directly related to the date of the last quarter of the moon, 

 for in 1898 the swarm occurred on July 9, and the last quarter of the 

 moon on July 10 ; while in 1899 the worm swarmed on July 1, and the 

 last quarter of the moon fell on June 29. In 1898 about two hundred 

 specimens of the worm were seen to swarm on the morning of July 8, 

 hut on the following day the animals appeared in vast numbers, while 

 on July 10 only about a dozen specimens could be found after a careful 

 search. In 1899 a wonderfully dense swarm appeared suddenly on the 

 morning of July 1, and only a few worms were to be seen on July 2, 

 after which they disappeared. As it was my habit to sail out upon the 

 ocean earlj^ every morning, I am certain that no other swarms than the 

 above-mentioned ones occurred between June 25 -August 19, 1898; 

 and May 17 -July 4, 1899. 



Description of the Swarming. — The swarming commenced very early 

 in the morning before sunrise, and soon vast numbers of the worms 

 were to be seen swimming upon the surface of the ocean. Few or none 

 of them were to be found in the shallow water near the shore of Log- 

 gerhead Key, but at some distance to the westward of the island, where 

 the water was between two and five fathoms in depth, they appeared in 

 astonishing numbers. The bottom at this place is of coral-sand, and is 

 covered with a sparse growth of Goi'gonians and Nullipore Alg«, while 

 nearer the shore the bottom consists of living coral and coral-rock with 

 but little sand. "When first observed, at four o'clock in the morning of 

 the days of the gi-eat swarms, the worms presented very much the ap- 

 pearance shown in Figure 1, Plate 1. They swam with great activity 

 and as near as possible to the surface of the sea. I estimate that there 

 may have been about two worms to each square foot of the ocean's 

 surface. The worms were not uniformly distributed, however, but were 

 scattered irregularly, sometimes congregating momentarily in wriggling 

 masses, such as were likened by Agassiz, in the case of the Fijian 

 Palolo, to " thick vermicelli soup." These congregations are not due to 

 any affinity for one another on the part of the worms, but are merely 

 the result of accident, for each individual worm swims about quite inde- 

 pendently of the others, and shows no tendency to remain in tlie presence 

 of any other which it may chance to meet in its wanderings. The 



