220 Dr. A. Korotneflf on Poljparium ambulans. 



To show the affinity of our form with other polyps, we 

 must refer all these peculiarities of structure to the common 

 characters of the polyp-type, and at the same time regard 

 them as definite results of a change brought about by special 

 needs. 



We commence with the tentacles : — Where ought these to 

 occur? Certainly either at each buccal aperture or at the 

 margin of the whole colony. A Mceandrina enables us to 

 decide this question. In this form we see individual polyps, 

 or more properly buccal cones, like those of Polyparium, dis- 

 tributed in bands on the surface of a globular polypary, the 

 buccal cones being arranged in a series exactly in the middle 

 of each band. In this way each band resembles a Polypariunij 

 but with the diflterence that the buccal cones occur in greater 

 number in the latter. But the most important thing is in the 

 distribution of the tentacles in Mceandrina ; these do not sur- 

 round each mouth-aperture, but stand along the margin of 

 each band. If we conceive that in a common Actinia a mul- 

 tiplicity of mouth-openings has been produced by their division, 

 we shall get a band-like, Mwandrina-likQ form in which also 

 the tentacles originate at the margin. In Polyparmm there- 

 fore we ought to seek for tentacles at the margin, and regard 

 them as having disappeared, such a disappearance being 

 explicable to a certain extent by change in the mode of life. 

 As a Mceandrina is an adherent organism it is, as regards 

 nourishment, under much less favourable conditions than 

 Polyparium ambulans, which can change its place with com- 

 parative rapidity • hence the tentacles are much more necessary 

 to Mceandrina than to Polyparium, although they are rather 

 rudimentary. 



As regards the buccal apertures, there can hardly be any 

 doubt that their number does not denote an individualization, 

 but rather a division, and the absence of an oesophagus at 

 each aperture somewhat strengthens this supposition. Such 

 a complete reduction of the tentacles and considerable increase 

 of the mouth-apertures not only has an influence upon the 

 external habit of the animal but also affects its internal 

 organization. In the first place we must here mention the 

 septa ; under such circumstances they must certainly be 

 subject to a fundamental alteration. That the septa of Poly- 

 parium must be homologous with the septa of a simple 

 Actinia we have already seen to be probable, nevertheless 

 their divergent form remains as a considerable obstacle. If 

 we imagine the oesophagus of a polyp to have disappeared, 

 the affair of the septa will certainly stand on quite a different 

 footing, they must be free in the interior of the gastral 



