176 Dr. H. Rauff on the Genus Hindia, Dune. 



look only upon tlie concave parts of the arms, while the con- 

 vex surfaces, and consequently the points of union, are turned 

 away from the observer ; we see in the transverse section th e 



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projection of the arms bounding the hexagonal meshes 

 (columns). Vfhcre the preparation is not quite clear it tlien 

 usually becomes impossible to determine whether the three 

 arms meeting to form a triangle belong to the same spicule or 

 to three different ones (see diagram, fig. 3), and thus it often 

 seems as if one head met the other, althougli this usually is 

 not the case; for where the image is clearer, and especially 

 where at the same time the transverse section bends a little 

 towards the eye, the mode of union above described appears 

 again more or less distinctly, and it is at least by far the 

 predominant one. From this also we learn why the trabecula3 

 generally appear thinner in the transverse than in the radial 

 section. It is still possible that both modes of union may 

 coexist; the diagram of the latter (in which, however, for 

 unity of construction the fourth ray must necessarily be more 

 or less developed) is shown in tig. 4 for the longitudinal 

 section. 



Without going further here into the question of the presence 

 of one or more stomachal cavities, and consequently as to the 

 morphological individuality of the animal, it may be mentioned 



