Echinodermaia, hy Prof. F. J. Bell. 437 



and of allied forms. The marked divergence in the statements 

 which I now have to make with regard to Fhormosoma iila- 

 centa from those made by two brilliant and accomplished 

 German naturalists with regard to an apparently allied species 

 is sufficient to show this. 



I should add that 1 have made some use of the material 

 obtained by H. M.S. ' Challenger,' but the unique condition of 

 some of the specimens, the disappearance of the viscera of 

 others, and the absence of the remarkable P. rigidam have 

 prevented me from making the investigation as complete as I 

 wished. 



In the interesting essay on the Echinothuriidfe *, which Dr. 

 P. and Dr. F. Sarasin based on the beautiful form Astheno- 

 soma urens, which they discovered off Ceylon, especial atten- 

 tion was directed to the organs of Stewart ; these are of con- 

 siderable size in the Ceylon species. Notwithstanding the 

 fact that no description of these organs has been given by 

 Thomson or Agassiz, the Doctors Sarasin ascribe to the Echino- 

 thuriida^ as one of their distinctive characters a " gewaltige 

 Entfaltung der Stewart'schen Organe," and they say, further, 

 " Sowohl die Cidariden als die Diadematiden besitzen die 

 Stewart'schen Organe, welche bei den Echinothuriden reich 

 entwickelt sind, in rudimentiirer Ausbildung." I was some- 

 what interested to discover how it was that organs so remark- 

 ably well developed had not been seen by previous observers. 

 The first example I opened served to settle the question on 

 the same principle as that on which Tilburina could not see 

 the Spanish fleet ; the organs of Stewart were not there to be 

 seen. In some anxiety to bring this state of things into 

 conformity with the very absolute statement of the Drs. 

 Sarasin I opened another specimen ; here I found the arrange- 

 ment shown in PL XVllI. fig. 2, which is drawn of the 

 natural size, the whole test being 110 millim. in diameter. I 

 come to the conclusion therefore that in Fhormosoma the 

 organs of Stewart may be present in a rudimentary or ves- 

 tigial condition, or may be absent ; I have been unable to 

 find any trace of their presence in Phormosoma bursarium or 

 P. tenue; but as these specimens have been several years in 

 spirit, I will not lay much stress on the apparent absence of 

 these organs. I need not do that to show that there is a con- 

 siderable difference in the anatomical characters of the two 

 genera, differences which most of us have tacitly assumed not 

 to exist, which, possibly, we had no reason to expect to see, 

 but as certainly no reason not to expect. 



* Ergebnisse uaturw. Forsch. auf Ceylon, I. 3. Ueber die Auat. der 

 Echinothuriden u. die Phylog. der Echiuodermen. 



