38 Mr. W. K. Spencer. On the Structure and [Mar. 2 



ossicles were said to be ambulacra] pores. This structure offers points 

 of resemblance to that of star-fish. Billings himself says, " I have 

 placed E. Bigsbyi in the order Asteriadae because the structure appears 

 to me more like that of the star-fishes than those of the Cystidese. 

 None of the Cystidese have ambulacra whose pores penetrate through 

 the covering of the body, and therefore all such genera as Edrioaster 

 Agelacrinites and Hemicystites belong to a very different division of 

 the Echinodermata. When we know more of their structure it is 

 probable they will be arranged as a sub-order for which the name 

 Edrioasteridse would be appropriate, as it would suggest their sessile 

 condition on the one hand and on the other their affinity to the 

 Asteriadse." Schmidt, in 1874, in his description of Mesites Pusireffski 

 points out the resemblance of Mesites to Edrioaster. He shows that 

 Mesites has a double series of plates, and that between the upper 

 series of covering plates are pores. These, however, lead only into 

 the ambulacral groove which is quite closed from the body cavity. 

 Schmidt on this ground cannot agree that Mesites, at any rate, has 

 any affinities with the Asteridaa. 



The theory that Agelacrinus and Mesites were connecting links 

 between the Cystideans and the Eleutherozoa was further advanced by 

 Neumayr. Neumayr (16, p. 420) supports his hypothesis by a state- 

 ment which he attributes wrongly in " Die Stamme des Thierreiches " 

 to J. Miiller. "Wohl weiss man durch die Untersuchungen des 

 grossen Zoologen und Anatomen Johannes Miiller, dass in friiher Jugend 

 auch bei den Seesternen die Ambulacralcanale innen liegen, und dass 

 da bei weiterem Wachsthume eine Aenderung in der Art eintritt, dass 

 sich nun erst die definitiven Ambulacral-platten bilden und die Wasser- 

 gefasse vom Innern abschliessen, wahrend der sie nach aussen 

 bedeckende Theil resorbirt wird und verschwindet." This double 

 series of plates present in the developing Asteroid is, according to 

 Neumayr, readily capable of interpretation by comparison with the 

 double series of plates in Mesites. 



An earlier paper shows that the authority for this statement con- 

 3erning the developing Asteroid was A. Agassiz. Professor Ludwig 

 has given a very complete account of the development of Asteroids and 

 kindly answering my inquiry categorically denies Agassiz's statement. 



Schmidt had already exposed the weak point in this theory, namely, 

 that there are no passages in Mesites which would compare to the 

 ambulacral pores of star-fishes. Mesites has now been definitely 

 relegated to the Diploporite Cystideans. The theory that Edrioaster 

 and Agelacrinus represent the Eleutherozoic ancestor has however 

 survived, and Bather* claims an independent status for this group as 

 definite ancestors of free-moving Echinoderms. 



* ' Treatise on Zoology,' Lankester, vol. 3, " Echinoderma," and in various other 

 papers. 



22, 





