350 JOHN F. PULTON, JR. 



Having considered the physical and chemical aspects of 

 the actinian pigments, what deductions can be drawn as to their 

 origin ? 



It is clear, inasmuch as there is no internal circulatory- 

 system between the ectoderm and entoderm, that the pigment 

 must be manufactured from substances of the outside world 

 which come actually into contact with the individual cells. 

 Likewise it is evident that these substances are absorbed from 

 within, carried, that is, in the chylaqueous fluid, since the 

 ectoderm of an anemone serves for protection rather than for 

 absorption. It is highly improbable that the pigment comes 

 directly as food (as Crozier (1917) holds for a species of polyclad 

 and Poulton (1893) for certain insects) ; if that were true, it 

 should exist in solution in the gastrovascular fluid ; but this 

 seems definitely not to be the case (MacMunn). The more 

 reasonable hypothesis, it seems to me, is that the cells con- 

 taining the colour themselves synthesize the pigment from 

 certain food substances. This means that in the absence of 

 a blood-system each actinian cell has to elaborate its own 

 pigment. 



Little is known concerning the nature of the food from which 

 the cells manufacture pigment. Various speculations, however, 

 have been made on this point, particularly in the case of the 

 insects. In this class of animals, as Poulton (1893) has shown, 

 the pigment of the body appears to be a modified chlorophyll. 

 That such a condition should obtain among the actinians seems 

 at first impossible. Many actinians live in an obligate associa- 

 tion with Zooxanthellae, an association in which the anemone 

 is probably parasitic upon chlorophyllous cells (Fulton, 

 1921 a) ; that is, in times of starvation they turn upon the 

 cells from which they possibly receive nourishment (by photo- 

 synthesis) and engulf them. Also in many actinians the 

 " yellow cells ' are lodged directly in the tissue of the ectoderm 

 and entoderm (Hertwig, 1883). It is a matter of common 

 knowledge, too, that actinians feed upon pelagic forms which 

 contain chlorophyll. From these facts it is evident that 

 actinians use chlorophyll as food. As has already (p. 348) 



