ZOANTHARIA 



opinion, a different incrustation in two otlierwise similar forms does not entitle ns to set up two 

 different species, and the incrustation thus theoretically is of no great value for the characterization 

 yet in practice, owing to what has been said above, it may be used to help in the characterization 

 of a species. 



Regarding the arrangement and appearance of the tentacles, they give at least in preserved 

 specimens no assistance in the identification of the species, the appearance and arrangement being 

 almost the same in all species of Zoanthidae. The number varies in different species but as it is 

 dependent on the number of mesenteries, it is of no practical importance for the classification. 



Even the structure of the oesophagus provides no basis for the identification of the species, as 

 it is fairly uniform. Whether it is elongated or not, whether the diameter is small or large, is 

 generally dependent on its more or less contracted state. The appearance of the siphonoglyphe is 

 only exceptionally of importance for the clas.sification, especially as in the Zoanthidae, in contrast to 

 what we find in the Ceriantharia, it is onh' the directive mesenteries which are always attached to it 

 The same applies to the prolongation of the siphonoglyphe (hyposulcus) which, at any rate in all species 

 examined by me, showed almost the same degree of development. 



As to the finer anatomical structure, the body-wall, especially the structure of the niesoglcea, 

 provides one of the best characters for the separation of the species, even though variations may 

 sometimes occur within the same species. The different sizes of the ectoderm, endoderm and mesogloea 

 in relation to each other should be fairly constant in the different species, whereas the size of the 

 germ-layers varies with the state of contraction. The ectoderm may vary greatly in appearance in 

 the different species but above all the appearance of the mesogloea is of importance for the 

 classification, as it either contains but few cells, or is provided with numerous cells, cell-islets or 

 lacunae arranged in a manner often very characteristic for the species. 



The appearance and structure of the sphincter help to characterize the genera but are not 

 always of such great importance for the separation of the species, though in a few cases very 

 characteristic sphincters occur. It must also be observed that there is a variation in the appearance 

 of the muscle, which at least in many cases may be connected with the state of contraction of the 

 sphincter. 



The number of the mesenteries gives a very good character for the separation of the species, 

 but the variations are not so unimportant, even in full-grown polyps. Furthermore, it has to be 

 mentioned, though already pointed out previously in discussing the capitular furrows, that the 

 mesenteries increase in number with age, so that only full-grown specimens of different species can 

 be compared with certainty. The breadth of the micro-mesenteries may vary in different species, 

 though this is fairly seldom, as it is generally of importance for the separation of species. It must 

 specially be pointed out, that in different species the breadth is compared at the same part of the 

 body, as for example the lower part of the oesophagus, the micro-mesenteries in the different parts of 

 the body being of extremely varying breadth, in the distal part well developed but tapering quickly 

 downwards. But even if we consider this, we run the risk of making mistakes in classifying, as the 

 state of contraction of the pylop changes the position of this zone very considerably. The appearance 

 of the longitudinal muscles in the mesenteries may often be very characteristic, but even here we 



