226 University of California Publications in Zoology [Vol. is 



fact that some commensal worms, such as Polynoe pulchra living on 

 the keyhole limpet between the foot and the mantle of the latter, and 

 protected from the light, are conspicuously colored. The same has 

 been observed to be true with Polynoe ocellata, which lives as a com- 

 mensal in tubes, sheltered from light, yet is very vividly colored. 



The so-called color mimicry in Polynoidae may be due to chemical 

 responses or to stimulating enzymes. The commensals living in close 

 contact with their messmates probably have a chemical inter-relation 

 with the latter, and are influenced by some of the same chemical con- 

 ditions which are responsible for the color production in the latter. 

 Under a similar chemical or enzymic reaction the same color pattern 

 is produced in the commensal polynoid. This may be a plausible 

 explanation of how commensal polynoids adopt the color pattern of 

 their messmates to such perfection as is shown in Polynoe pulchra 

 living on the holothurian, and Polynoe scolopcndrina living in the 

 tube of the Lysidice, both mimicking the color of their messmates. 

 These facts seem to lead to the conclusion that there must be some 

 chemical interaction between the two commensal species stimulating 

 the latent chemical and protoplasmic properties of the worm to color 

 production. That animals can be stimulated to produce colors has 

 been proved experimentally by extracting the pigment-producing 

 enzymes from beetles and placing parts of other unpigmented beetles 

 in the extracted enzymes, with the result that pigment was produced 

 on the unpigmented beetle (Tower, 1906). Evidently some influence 

 must be exerted by the enzymes of the host on the commensal worms 

 and the chemical complexes which are present in the protoplasm of 

 the commensal, when stimulated in the polynoid, will react in a definite 

 manner, producing similar colors to those of the host. 



The great differences in coloration between Polynoe pulchra living 

 on the keyhole limpet, and the one living on the holothurian may be 

 explained on the basis that although the former is living in the mantle 

 fold of the limpet in an area which shows no pigmentation, yet the 

 pigment-producing enzymes are probably present in other parts of 

 the body of the moUusk. The cells of the lower surface of the latter 

 may not have the base, or the color-producing properties and hence 

 do not respond to the stimulus of the enzyme, while the protoplasm of 

 the polynoid possesses the color producing properties which are latent. 

 As soon as they receive the proper stimulus, they react and the dark 

 brown or black pigment, similar to that found on the upper surface 

 of the mollusk, is produced in certain areas of the elytra of the poly- 



