ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 301 



The Atlantic Palolo swarms at the surface before sunrise within 

 three days of the day of the last quarter of the moon between June 29 

 and July 28. The posterior, sexually mature end of the worm breaks 

 away from the anterior end, and swims backwards with great rapidity 

 until about the time of sunrise, when it contracts, casting the genital 

 products into the water. The anterior part remains in the coral rock. 



The worm requires at least two years to attain sexual maturity. 

 There are 57 p.c. of males and 43 p.c. of females. Only sexually 

 mature forms cast off their posterior ends at the time of the swarm. 

 Immature forms are about twelve times as numerous. 



Cracking the coral rock induces premature expulsion of the genital 

 elements. Eggs obtained in this way are immature and cannot be 

 fertilised, even twelve hours before the time of the normal swarm. All 

 the eggs mature simultaneously at that time. 



The normally liberated eggs float in the water, and begin to segment 

 soon after extrusion. The segmentation is total and unequal, the 

 gastrula is formed by epibole, and the larva is telotrochal. The young 

 larvse swim near the surface, but sink to the bottom upon attaining four 

 pairs of setigerous lobes. The posterior segment of the larva bears a 

 pair of dorsal as well as a pair of ventral cirri. Only the ventral pair 

 of cirri persist in the fully developed worm. 



Fresh-water Polychasts.* — Ch. Gravier notes that four families of 

 Polychasts have representatives in fresh water. Among the Nereida3 

 there is Lycastis ouanaryensis Gravier from French Guiana. Mature 

 female specimens were found in fresh water, but without the normal 

 epigamous transformation. The Eunicidas are represented by Lumbri- 

 conereis, found by Kennel ; the Capitellidae by Eisigella ouanaryensis 

 Gravier ; and the Serpulidas by Manayunlcia speciosa Leidy, Caobangia 

 billeti Giard, Dyboivscella godle/rskii and D. baicalensis Nusbaum. 



Otocysts of Polychaeta.* — P. Fauvel has studied the otocysts which 

 are especially characteristic of the Sabellidge. They occur also in some 

 Terebellidffi, in Arenicolidag, in two or three Ariciidas, and in some 

 Alciopidae. 



In Polychaets, as in Crustaceans and Molluscs, there are two kinds 

 of otocysts : — (1) those remaining in communication with the exterior 

 by a ciliated canal, and enclosing otoliths composed of foreign bodies 

 {small grains of quartz) ; (2) those which are completely closed, and 

 enclose spherical otoliths, with concentric layers, of an organic nature, 

 and secreted by the organ. In these closed otocysts there may be one 

 otolith or several. 



The otoliths are moved by the play of vibratile cilia, except in 

 Arenicola grubii and A. ecaudata where cilia are entirely absent. In the 

 last case there is indeed always movement, but it is a brownian move- 

 ment. In Amphitrite edwardsi there are no otocysts, but small encysted 

 Trematodes have been described as such. 



Notes on Polygordius.J — P. P. Cowles notes that larvae of Poly- 

 gordius appendicidatus are abundant at Woods Hole, Newport, Beaufort 



* Comptes Rendus, exxxv. (1902) pp. 784-6. + Tom. cit., pp. 13G2-5. 



\ Johns Hopkins Univ. Circ, xxii. (1903) pp. 21-2 (1 pi.). 



June 17th, 1003 x 



