10 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
it is interesting to notice that according to Wilson (’92, p. 372) the 
males of Nereis outnumber the females to a very remarkable degree, while 
in Staurocephalus gregaricus, 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 
insure this; but where the egg-laying period isa long one, and there 
are not often great concentrations of individuals, the males must out- 
number 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, Florida, 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 
prevail 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 under such conditions a 
large number of young larve 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 Annelids. 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 
