258 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



in spiral; head very slender, mouth far back from anterior extremity 

 (Fig. 29). 



Size. Large individuals exceed 1 m in length, with a diameter of only 

 2-5 mm or less. Body is very strong and not easily ruptured. 



Color. Pale flesh color, pale ocher, or straw color, more rosy in an- 

 terior portion, grayish posteriorly. Small individuals grayish white or 

 almost colorless. 



Ocelli. Absent in mature worm ; a single pair present in larval stages. 



Nephridia. The peculiar metanephridia (Fig. 30) of this species are 

 large and very numerous (Coe, 1930). 



Habitat. Beneath stones in hard sand or clay fully exposed to surf. 



Distribution. At present known only from Montara, California, and 

 southward to Ensenada, Mexico. 



Regeneration. Individuals of this species are remarkably hardy under 

 laboratory conditions, living for several months in vessels of sea water 

 which is changed occasionally. Posterior regeneration occurs readily, but 

 attempts to obtain anterior regeneration and regulation from body frag- 

 ments have not thus far proved successful. Such fragments may, however, 

 remain alive for several months, during which time the organ systems 

 present become simplified and much reduced in size. 



Reproduction. During the spring and summer months individuals 

 may be found with mature sexual products. If several individuals are 

 placed together in a vessel of clean sea water, a large number of fertilized 

 eggs may be deposited in strings of mucus during the first or second night 

 after the worms have been collected. Otherwise, eggs may be obtained by 

 cutting the body of a ripe female. Sperm may be added after washing the 

 eggs several times in clean sea water. Development of the direct type pro- 

 ceeds rather slowly, several daj's being required before the young larva 

 leaves the egg membrane. About a month after fertilization the organiza- 

 tion of the adult worm becomes fully established if the lai-va has been 

 suitably fed with mixed cultures of diatoms and other included organisms. 



11. Procephalothrix spiralis (Coe), 1930 



(Plate 28, fig. 37) 



Cephalothrix linearis (Rathke) Coe, 1905; C. spiralis Coe, 1930. 



Body. Filiform in extension, coiled spirally on contraction ; head very 

 long, acutely pointed, mouth situated far back of brain (Fig. 37). 



Size. Length, 5 to 15 cm when extended; usually only 1-1.5 mm in 

 diameter. 



