218 University of Calif ovnia Puhlications in Zoology [Vol. 18 



That the environiiient and adaptation may lead to some extreme 

 variations is illustrated by the shape of Polynoe ocellata. This species 

 has been recorded from Japan (Mcintosh, 1900; Izuka, 1912) as a 

 commensal, living in the tubes of Spirochactoptenis challcngcna. 

 The worm is extremely elongated and narrow, having over one hun- 

 dred segments and fift}^ or more pairs of elytra. The length of the 

 worm is about 60 mm. but its breadth is only 2.5 mm., including 

 setae. It is most vividly colored with yellow, olive, black and white 

 markings. The elytra are exceedingly small, translucent and smooth. 

 The first pair of elytra, however, are large, covering the prostomium 

 completely ; they are also less delicate. In a vertical section, Mcintosh 

 discovered that the cuticle and hypodermis of the worm are unusually 

 thin. This again illustrates the great variability and the power of 

 adaptation of this polynoid. It is remarkable that the external 

 changes do not occur uniformly but that parts subjected to somewhat 

 different environment, as the anterior elytra, which are naturally 

 outside of the tube and are exposed to the free ocean water, differ in 

 size and structure. 



As far as is known it may be considered as a general rule that 

 the commensals are usually larger in size than the free-living indi- 

 viduals of the same species, provided the dwelling place of the com- 

 mensal is sufficiently large so as not to interfere with the expansion 

 of its body. Polynoe californica is known as both commensal and 

 as free-living. The commensal animals are noted for their large size, 

 while the free-living individuals collected from various places are 

 much smaller. All the largest specimens, except one from Santa 

 Catalina, were collected near San Pedro. They range from 35 to 45 

 mm. in length and from 8 to 14 mm. in breadth. The specimens from 

 other localities have a size ranging from 15 to 30 mm. in length and 

 from 5 to 11 mm. in breadth. The average length of the worm is 

 about 25 mm. Johnson (1897) states that the species has been found 

 on a huge Amphitrite off San Pedro. That the commensal forms of 

 Polynoidae are usually larger in size, relatively and absolutely, can 

 be proved by the fact that not only individuals of the same species 

 distinguish themselves through their larger size from the free-living 

 specimens, but tliat species which are known exclusively as commensals 

 are of relatively greater size. Thus the largest species in the family, 

 Lcpidastheivia gigas, is a commensal with an amphitrite. The largest 

 specimens measure 180 mm. in length, and 7.5 mm. in width. It would 

 be a far-reacliing conclusion to assume that Lepidasthcnia gigas has 



