MAYER: STAUROCEPHALUS GREGARICUS. i git 
occurred on January 9, 1893, and their swarming probably had no 
relation to this event. 
Among worms, where certain segments of the body became sexually 
mature while others remain immature, or non-sexual, we find an inter- 
esting series of gradationsin complexity. Beginning with Staurocepha- 
lus gregaricus, where the sexual and non-sexual segments are exactly 
alike in external appearance, and where the entire worm swims at the 
surface at the breeding period, the next advance in complexity is met 
with in Palolo viridis, where, according to Friedlander (1898) the non- 
sexual segments are very different in appearance from the sexual, and 
where the sexual segments break off from the anterior portion of the 
worm and swim about during the egg-laying period without a head. 
Most complex of all are the cases of Autolytus, Filigrana, Myriana, 
Procerza, Syllis, etc. (see A. Agassiz, 62; Malaquin, ’93, etc.), where 
the sexual segments acquire a head, and eventually become free swim- 
ming worms, thus producing an alternation of generations. 
It seems probable that Staurocephalus gregaricus and Palolo viridis 
have independently acquired quite similar breeding habits through the 
agency of similar influences of natural selection ; although it must still 
be admitted that there remains a possibility that both worms may have 
descended from a remote and common ancestor that possessed some such 
breeding habits. 
The following table will serve to illustrate the principal points -of 
relationship in the breeding habits of the two worms : — 
Tar Atiantic “ PaLowo.” Tue Paciric PaLo.o. 
Palolo viridis, Gray, 1847. 
Staurocephalus gregaricus, Mayer. 
Lysidice viridis, Cotiin, 1897. 
On July 9, 1898, and July 1, 1899, 
the worm swarmed in vast numbers, 
The worm swarms in great num- 
bers, for breeding purposes, at Samoa 
for breeding purposes, at the Dry 
Tortugas Islands, Florida. The last 
quarter of the moon occurred on July 
10, 1898, and June 29, 1899. 
The 25-30 anterior segments of 
the worm contain no sexual ele- 
ments, the eggs or sperm being 
found in the posterior body seg- 
ments. The anterior segments, how- 
and Fiji, upon the mornings of the 
day of, and the day preceding, the 
last quarter of the October and No- 
vember moon. (See Whitmee, 1875 ; 
Friedlander, 1898.) 
According to Friedlander, 1898, 
a number of the anterior segments of 
the worm contain no sexual elements, 
these being found in the posterior 
body segments. The anterior seg- 
