NO. 3 HARTMAN : POLYCHAETOUS ANNELIDS 327 



calif ornica (p. 349) and Sabellaria cementarium (p. 340), agree on the 

 whole with those of S. alveolata described by Wilson ( 1929, pp. 221-270). 

 The eggs of P. calif ornica are purple in mass and measure about 70 ju, in 

 diameter; those of S. cerjientarium are deep pink in mass and somewhat 

 smaller. They are covered by a thin membrane, hardly visible even after 

 fertilization. In P. calif ornica swimming larvae develop about 12 hours 

 after fertilization, and in 24 hours the typical parts of the trochophore 

 are visible. The prototroch is well developed, but incomplete middorsally ; 

 the telotroch is weak, and apical cilia are few. After 2 days the larva has 

 acquired about 5 pairs of long, spinose, natatory setae, and the alimentary 

 tract is clearly visible because of its long, beating cilia and the large, 

 humped, gastric portion. After 2 or 3 days a characteristic color pattern 

 appears, consists of widely spaced, yellow-brown, epithelial cells (pi. 29, 

 fig. 15), and on the oral side there is a greatly flattened equatorial disk. 

 A pair of eyespots is usually visible after 2^ to 3 days. The lateral oral 

 lappets are long, and the great extension of the equatorial disk on the oral 

 side gives the larva a lopsided appearance. 



Long, spinous (pi. 29, fig. 16) setae, greatly exceeding the larva in 

 length, emerge from paired, fleshy, lateral lobes, the so-called setal sacks; 

 they are postoral in position, but the sacks extend far up in the hood 

 (pi. 29, fig. 15). As the larva increases in size, the number of setae is 

 gradually increased to 30 to 50 on a side. They are held stiffly, in a fas- 

 cicle, at the sides of the body when the larva is swimming, but are thrust 

 outward and foi-ward when disturbed or stopping in its forward progres- 

 sion. This brings the setal sacks in position nearer the mouth and tends 

 to push the latter shut. This segment is unique in its precocious develop- 

 ment in larval life and the major role it comes to have in the adult, since 

 it is (at least primarily) the forerunner of the operculum and its stalk. 

 During planktonic, lai^val life it occupies a normal position, posterior to 

 the oral aperture, its setae directed back or laterally. During metamor- 

 phosis certain portions of this segment grow rapidly so that it is perma- 

 nently pushed forward (pi. 29, fig. 17), on the dorsal side of the mouth, 

 extends forward beyond it, its provisional long setae gradually replaced 

 by the 1, 2, or 3 kinds of paleae which characterize the adult opercular 

 crown. Thereafter this segment is permanently forward. The neuro- 

 podial portion of one of the larval somites (see above, p. 325) remains 

 postoral and comes to be the first anterior thoracic segment. 



During early larval life the ventrolateral edges along the prototrochal 

 area grow out to form a pair of long, prehensile tentacles. They are partly 

 covered with short cilia and are pigmented in their distal third. These 



