354 JOHN F. FULTON, Jll. 



commensal with the (jraiige colonies of Ecteinascidia 

 turbinata and the purple colonies of Ehodozona picta 

 are themselves orange and purple, respectively, and of a shade 

 very similar to that of the animal with which they are com- 

 mensal. On starvation (i. e. when removed from the colony 

 of tunicates) these polyclads lose their colour, but when 

 allowed to feed again with the tunicate colonies they regain 

 their colour in a very short time. This, Crozier believes, is an 

 example of a pigment which is formed directly from food, and 

 it accounts for the colour being the same as that of the animal 

 with which the polyclad is commensal. The writer has made 

 certain other observations which in part support Crozier's 

 conclusion. The colouring matter in the tunic of Ectein- 

 ascidia turbinata is made up of stellate orange chromato- 

 phores. Now, if the body-cavity in one of the polyclads 

 recently taken from a colony of Ecteinascidia be observed 

 under the microscope, not infrequently small pieces of orange 

 pigment can be observed, many of which show clearly that they 

 are portions of the chromatophores from the tunic. Owing 

 to the great frailty of the polyclads, the fate of these small 

 pieces of pigment could not be followed completely ; as a result 

 it was impossible to settle definitely whether the j^igment was 

 ingested bodily by the entodermal lining as Congo red is ingested 

 by the young of Convoiuta roscoffensis (Gamble and 

 Keeble, 1903), or first went into solution. If the former 

 assumpti(m were true, it might be possible to raise a race of 

 colourless individuals of this species (as Poulton, 1893, has 

 done for certain of his insect larvae) by preventing their 

 association with Ecteinascidia. The writer, however, is in- 

 clined toward the belief that the fragmentary pieces of chroma- 

 tophore go into solution in the water-vascular system and 

 are subsequently taken up by the cells which need them. The 

 latter explanation, if correct, would accord with the fact that 

 the pigment does not extend promiscuously over the body, but 

 is found in definite and regular designs. 



Among some Turbellarians (Convoiuta and Vortex) the green 

 or yellow colour is occasioned by the presence of symbiotic algae. 



