39 



if completely resorbed, would leave us a sheathed spine identical with the sheathed 

 spine of the Echinothuriæ; the existence in that family of club-shaped primary 

 spines as in Phormosomu biirsaria (iiin), the tip of which is still sheathed to a 

 certain extent, shows how close is the relation of the sheathed spines to true pedi- 

 cellaria^". — I am decidedly opposed to this reasoning. The sheathed spines in 

 Asthenosoma are spines of the structure typical in Echinothurids : beautifully fenestrated 

 tubes ending in a fine point. In the „sheathed" pedicellariæ of Aspidodiadeina (and 

 of all Diademulidœ) the stalk is of an irregular structure quite dilTerent from that 

 of the spines of the Echinothurids (or of any other Echinids), and even when the 

 head of these pedicellariæ disappears, they do not get more accordance in structure 

 with the spines, and they never can be homologized with the sheathed spines of 

 Asthenosoma. The clubshaped spines of Phonnosoma biirsarium etc. are also true 

 spines and can not present any proof whatever of the close „relation of the 

 sheathed spines to true pedicellariæ". Upon the whole I must confess that I cannot 

 see any evidence of the pedicellariæ of Echinids being only transformed spines. In 

 the Asterids, to be sure, there can be no doubt that some forms of pedicellariæ 

 are transformed spines; but that that is true for all of them, I am not convinced 

 (e. g. those o{ Asterias). The figures given of their development by Agassiz (Embryo- 

 logy of the Starfish. PI. VIII. figs. 2 — 4) are much too undetailed to show them to 

 be transformed spines, nothing definitely being seen there of the formation of the 

 calcareous valves. But especially with regard to the pedicellariæ of Echinids no 

 proof at all has been produced, showing them to be transformed spines. In fact 

 the only argument produced by Agassiz in favour of this supposition is „the case of 

 tripartite, pedunculated, Echini pedicellariæ attached as common spines are, upon a 

 tubercle, surrounded by the peculiar smooth area called the scrobicular circle" as 

 is found in Podocidaris^). I cannot find any proof of the homology herein. As is 

 well known, the scrobicular circle is only the impression of the muscular coat at 

 the base of the spines; in large spines it is very distinct, in small ones indistinct 

 or not to be seen at all. All pedicellariæ are attached to small tubeicles and sur- 

 rounded by a muscular coat at the base, just as in the articulation of the spines, 

 only much more delicate. A scrobicular circle may certainly be found in many 

 Echini around the tubercles of the larger pedicellariæ. But from this fact it only 

 follows that pedicellariæ and spines are articulated in the same manner to the test, 

 not at all that they are homologous. Neither can I see the least proof of their homology 

 in the fact that the spines of Echinidæ present differences „fully as great as those 

 observed in the pedicellariæ" (Rev. of Ech. p. 669). It must be emphazised that no 

 transitional forms are found between pedicellariæ and spines in Echinids; likewise 

 the development of the pedicellariæ in Echinids is quite dilTerent from that of the 



') Rev. of Echini, p. GG9. 



'') Comp, tlie Ingolf-Echinuidea I. p. (i. FI. Xll. 'M etc. 



