ANTHOZOA OF THE WOODS HOLE REGION. 227 



thrust out of special pores, cinclides, or through improvised openings in the tissues of 

 the body wall. 



The marginal portion of the oral disk bears the tentacles, which are usually hollow 

 outgrowths from this part of the body. They vary greatly in size and number in 

 different species and genera. In Cerianthidae they form two distinct sets, the cir- 

 cumoral, surrounding the mouth, and the marginal, corresponding to those of other 

 orders. The latter are often designated as primary or principal tentacles; the former 

 as accessory or circumoral. 



As indicated above, the general form of the body as a whole is more or less cylin- 

 drical. Peculiarities of distinction will be considered in connection with those species 

 exhibiting them. This will also be the case in reference to particular features of oral 

 or pedal disks. In many of the orders some form of skeleton, calcareous or homy, is 

 present. This is particularly the case with most corals and alcyonarians. On the 

 other hand, most or all actinians are entirely devoid of anything of the sort. 



Another feature of some significance is the habit of certain actinians to expand 

 and inflate the pedal disk ar^l thus convert it into a float by means of which they are 

 able to migrate under the influence of currents, much as do certain other pelagic 

 coelenterates (Vesalia). This has been observed in several local species, and it seems 

 not unlikely that it may be of more general occurrence than might be supposed. 

 Among those which exhibit the phenomenon may be mentioned Sagartia lucioe, S. 

 leucolena, and Anemonia sargassensis. It should be stated, however, that this has 

 been noted only in specimens in the aquarium; but its occurrence under these condi- 

 tions with more or less frequency would strongly suggest its occurrence in nature under 

 certain circumstances. 



COLORATION. 



In comparatively few classes of animals are there richer or more varied exhibitions 

 of color than among Anthozoa. This is particularly striking in the tropical or sub- 

 tropical species. To those who may have had the exquisite pleasure of looking upon 

 the splendid display of colors associated with coral reefs no emphasis will be needed on 

 this point ; and to others an adequate verbal description would seem highly exaggerated. 

 The profusion of coloration and the plantlike features of many of these coelenterates 

 are doubtless the occasion of such names as anemones, anthozoa, zoophytes, etc., by 

 which many of them are known even to this day. 



Into the problem of the origin or significance of colors in these lower classes no 

 attempt will be made to enter seriously. Something of this has been done by the 

 writer in an earlier paper (1904) and to a less extent in a report on the Medusae of Woods 

 Hole (1905). However, there are some points of particular phases of color involved in 

 Anthozoa which call for notice. In the first place, it is interesting and significant that 

 among these creatures color is due to distinctly different factors. For example, Duerden 

 (1905) has shown that among many corals the dominant color is due to the presence 

 of commensal algae, Zooxanthellce, which thrive in the entodermal tissues of the polyps. 



