ECHINOIDEA. I. 



not the same as what Rothpletz has made of it. At all events Hesse is right, when he says that 

 the cancellate> structure is only < compliciertere Wachsthumserscheimmgen an Stacheln seines zweiten 



Bauplanes, so dass die Stacheln ein mid derselben Species, z. B. von Strongyloccntrotus albus Ag 



je nach dem Stadium ihrer Verdicknug theils zn den Radiaten, theils zu den Cancellaten zu rechnen 

 sein wiirden (op. cit. p. 192). - To judge by what has hitherto been brought to light, we may scarcely 

 expect to find features of any greater systematic importance in the structure of the spines with regard 

 to the forms treated of here. 



The gills will scarcely present peculiarities that may be used as systematic characters of 

 greater importance. They generally contain some irregular spicules and fenestrated plates, which are 

 in the lower part rather large and pass evenly into the plates of the buccal membrane; towards the 

 ends of the branches they become smaller and more irregular, at last only branched calcareous needles. 

 Common bihamate spicules are most frequently found together with these, sometimes in very great 

 numbers (Pseudobolctia}. Heterocentrohis and Coloboccntrotus are distinguished by having pedicellarise 

 on the gills (placed on the larger fenestrated plates). In Stomopneustes only small three-radiate spicules 

 are found in the gills (PI. XVII. Fig. 13). -- The spheeridice are very similar; their shape, number, or 

 position can in no way be used as distinguishing characters between species, genera, or greater groups 

 within this division of the Echinids. 



The buccal membrane may be covered with plates, or naked, and this feature has played no 

 small part in the classification, and will also persistently be of importance. It is, however, to be 

 observed that it cannot always be seen directly whether plates are found in the buccal membrane or 

 not. Often it looks quite smooth and naked --as for instance in Echinus acutus but if a piece of 

 it is cleared in potash or Canada balsam, it is seen to be quite full of larger or smaller, simple fenes- 

 trated plates; only when these plates carry pedicellarise they become more complicate, and may then 

 be seen on the dried skin. Thus a microscopic examination is necessary in order to ascertain whether 

 plates are found in the buccal membrane or not. Most frequently among the fenestrated plates more 

 or fewer spicules of the common bihamate form are found. The part inside of the buccal plates gene- 

 rally contains numerous smaller fenestrated plates, arranged more or less radially; these plates are 

 upon the whole more simply constructed than those outside the buccal plates. In several species the 

 buccal membrane is almost or quite naked (with the exception of the buccal plates), for instance 

 Echinus magellanicus, albocinctus, Robillardi. In some species small spines are found on the buccal 

 plates (for' instance Ech. csculentus\ and in Pseudoboletia, Heterocentrohis, and Colobocentrotus spines are 

 even found in the plates of the buccal membrane outside the buccal plates. 



The inner anatomical structures are especially little known in the different genera, with the 

 exception of the dental apparatus and auriculae. These, however, show a so similar structure, that 

 important differences that might be of systematic significance, are scarcely to be found, and as to the 

 other anatomical features, it is still more improbable that here should be found differences of any 

 importance apart from the fact that it would be very unpractical, if the inner anatomy was to be 

 much used in the classification. Thus we have only left spicules and pedicellariae but here we also 

 find what we want. 



