64 N. AnnANDALR: The Fauna of Brackish Pouth. [VOL. I, 



between the typical SagaYtia-X\\^Q young and the Ccrianthus-like 

 adult, while the internal anatomy, allowing for differences due to 

 maturity, was found to be identical in large and small individuals. 

 Moreover, although the basal disk had almost disappeared, it had 

 not altogether lost its function as an organ of adhesion, for man}' 

 large individuals dug from the mud were found on close examina- 

 tion to be adherent by their bases to shells and other small objects. 

 In preserved specimens it would often appear on superficial ex- 

 amination that the basal disk is in much the same condition 

 of atrophy as it is in Edivardsia and other burrowing forms, but 

 in living examples it is always clear that this is not the case ; 

 in fact, a distinct disk is present (plate iii, lig. 3), but it is rela- 

 tively small and in other respects degenerate. 



Stoliczka noted that the typical form of the species was able 

 to survive exposure to the sun out of water for some hours — a pheno- 

 menon which has been recorded in other Actinians — and I am able to 

 confirm his observation. When exposed at low tide the animals 

 remain with their tentacles extruded, and the whole organism has 

 a particularly flabby appearance. A close examination of hving 

 specimens under these and other conditions, and a comparison 

 with dead and carefully preserved material, enables me to suggest a 

 reason for the powers of endurance possessed by the typical 

 M . schillerianum ; possibly this explanation will be found to 

 appl}' to other species also. I have alread}" remarked on the com- 

 paratively thin walls of the column of the new race of M . schil- 

 lerianum as compared with those of the same part of the body in 

 the typical form of the species, and on the fact that it is possible to 

 gauge the thickness of the wall in small living specimens of the 

 former owing to its transparency. The wall of the column in the 

 typical form is usuall}^ less transparent than it is in the variet}^, 

 owing to the large number of zooxanthellse present in the endo- 

 derm ; but this very fact makes it possible to estimate the extent 

 to which the thickness of the wall is due to the layers other than 

 the endoderm. This can be done most easily by watching an 

 acontium which is being thrust out of one of the cinclides. It is 

 not difficult to see that the thin white thread has to traverse a con- 

 siderabh' greater extent of transparent tissue outside the coloured 

 endoderm than could be accounted for if the thickness of the ecto- 

 derm and mesoderm seen in a transverse section of a preserved 

 specimen were the same as the thickness of these same layers 

 during life. The shrinkage, which is inevitable in preserved speci- 

 mens, is very much more marked in the case of the typical form 

 than in that of the pond race ; it is less evident, in the case of the 

 former, if specimens are killed and preserved in weak formol than 

 if they are treated with reagents, such as corrosive sublimate and 

 alcohol, which give a more satisfactory result as regards cellular 

 histology. The reason for this apparently is that an aqueous solu- 

 tion of formol while causing intense muscular contraction during 

 life, does not dehydrate the tissues after death. If a specimen of 

 th -' typical form which has been preserved in formol be cut in two 



