10 BULLETIN: MUSEUM OF COMrAEATIYE ZOOLOGY. 



it is interesting to notice that according to AA'ilson ('92, p. 372) the 

 males of Xereis outnumber the females to a very remarkable degree, while 

 in Staurocephalus gregarious, and in the Pacific Palolo, the males and 

 females are about equal in numbers each to each. It is most essential 

 for the perpetuation of the species that the fertilization of the ova 

 should be insured. A very few males placed near to the females will 

 iusui-e this ; but where the egg-laying period is a long one, and there 

 are not often gi'eat concentrations of individuals, the males must out- 

 nuniber the females in order to make certain that the ova of any given 

 female may be fertilized. 



The egg-laying period of Staurocephalus gregaricus occurred in 1898 

 and 1899 upon days very close to the day of the last quarter of the 

 June-July moon. At this time, in the Tortugas, Floi'ida, the summer 

 is well established, the trade winds are no longer steady or boisterous, 

 and the calm weather that precedes the hurricane season has set in. 

 It is interesting to notice that very similar meteorological conditions 

 pi'evail in Samoa and Fiji, in October and November, — the months of 

 the swarming of the Palolo. 



My friend, Dr. Charles B. Davenport, has called my attention to the 

 fact that the advantages derived from a short egg-laying season are in 

 some measure offset by the circumstance that imder such conditions a 

 large number of young larvae are suddenly produced, and that therefore 

 the struggle for food must be greatly increased. To counterbalance 

 this difficulty, however, we have the interesting fact that while the eggs 

 of Nereis contain but little yolk, the eggs of Staurocephalus gregaricus 

 are heavily laden with yolk material. 



When we learn more concerning the egg-laying habits of Annelids, 

 there will no doubt be a number of species found that possess such 

 swarming habits as those of Nereis, and perhaps a few may be dis- 

 covered in which the breeding season is as short as in Staurocephalus 

 gregaricus and Palolo viridis. In 1893, while acting as assistant to Dr. 

 Alexander Agassiz upon the " Wild Duck " Expedition to the Bahama 

 Islands, I had the opportunity of observing the swarming of an Annelid. 

 We were anchored off Watlings Island (San Salvador) on the night of 

 January 15, and in Clarence Harbor, Long Island, on the night of 

 January 16. On both of these nights the surface of the sea was covered 

 by thousands of little Amielids. They were translucent, and had large 

 red eyes. They appeared to be congregating for breeding purposes, and 

 were breaking into pieces, so that we often found fragments 50 mm. in 

 length swimming about without a head. The last quarter of the moon 



