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 horny, 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 an,d 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 lucuje, S. 
leucolena, and Ammonia 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, Zooxanthell<z, which thriVe in the entodermal tissues of the polyps. 
