MAYER: STAUROCEPIIALUS GREGARICUS. 



11 



occurred on January 9, 18'J3, 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 gradations in 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 ai'e very different i)i 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, Myriaua, 

 Proceraja, 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: — 



The Atlantic " Palolo." 

 Staurocephalus gregaricus, Mater. 



On July 9, 1898, and July 1, 1899, 

 the worm swarmed in vast numbers, 

 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 Pacific Palolo. 



Palolo viridis, Gray, 1847. 

 Lysidice viridis, Collin, 1807. 



The worm swarms in great num- 

 bers, for breeding ]iurposes, at Samoa 

 and Fiji, upon tlie mornings of the 

 day of, and tlje day preceding, the 

 last quarter of the October and No- 

 vember moon. (See Whitmee, 1875 ; 

 Friedlander, 1898.) 



The 25-30 anterior segments of 

 the worm contain no sexual ele- 

 ments, the eggs or sperm being 

 found in the posteri(jr body seg- 

 ments. The anterior segments, how- 



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- 



