ECHINOIDEA. I. 



stages of the large ones of the same kind. Duvernoy') even thmks all the different kinds of pedicel- 

 larise to be developmental stages of a single, definitive form, pedic. tridens. Valentin (Op. cit. p. 49) 

 writes of the triph3-llous pedicellarice: < Je n'ai pu m'assurer si ce sont des pedicellaires d'nne espece 

 particuliere, ou s'ils ne sont que le jeime age des pedicellaires ophicephales:>, and Agassiz, in ^ Rev. 

 of. Ech. p. 665, says: cin Echinomctra there is no doubt these trifoliate pedicellariae are only the 

 younger stages of the tridactyle forms \ Scarceh- any student of these forms will now-a-days suppose 

 one form of pedicellariae to be a developmental stage of the other. On the other liand it must be 

 admitted that at a first glance the small pedicellarise might appear to be developmental stages of the 

 larger ones of the same kind. A little reflection, however, will immediately show the improbability 

 of this supposition; what re-arrangements were to take place in the calcareous mass to make a .small 

 fully formed pedicellaria become a large one! — Pedicellarise are not rarely found that seem either 

 to be only half-formed, or half-decomposed. The possibility that they might be somewhat decomposed, 

 because the preserving fluid had become acid, has to the dismissed at once, — if this were the case the 

 lime would be corroded everywhere, and not only the outer edge be decomposed. Doderlein (116) 

 has seen and figured such half-formed pedicellarise of Stcrcocidaris grandis and <.<Lciocidaris^. vcrticillafa, 

 and regards them as a separate kind. «Es scheint noch eine vierte Form von Pedicellarien bei den 

 Cidariden zu geben, von der ich aber bisher nur einige isolierte Klappen gesehen habe, die sicli auf 

 Praparaten ganz vereinzelt neben den anderen P'ormen fanden. Diese ; korbformigen Klappen zeigen 

 eine sehr weite, bauchige Kammer, die am oberen Theil in einer sehr grossen Offnung miindet; diese 

 Offnung zeigt einfache diinne und etwas gekerbte Rander; von Zahnelung u. dgl. ist keine Spur vor- 

 handen. Solche Pedicellarien erreichen bei C. grandis die Grosse und die iiussere Gestalt der dick- 

 kopfigen Form, sie sind dagegen sehr klein bei L. vcrt.icillata\ bei anderen Arteu kenne ich sie nicht, 

 audi ihren Standort konnte ich nicht entdecken (op. cit. p. 33). For a long time I had no clear under- 

 standing myself how to interpret this form, until I found some specimens of Plwrniosoina placenta 

 possessing such structures in large numbers and in different sizes, and then there was no doubt that 

 they are developmental stages of pedicellariae. On PI. XII, figs. 15, 24, 30, 38 the development of a 

 triphyllous pedicellaria is given. The part first formed is the basal part of the three valves and the 

 stalk (its upper end); they seem to appear contemporaneou.sly. From the basal part then the lilade 

 grows up, and new calcareous particles being constantly added all round, it grows in breadth and 

 height; the apophysis is early formed. The figures give, better than a long description, an idea of 

 the way in which the growth takes place. Where a distinct margin is formed the growth is com- 

 pleted. The margin is first formed below when the definitive breadth has been reached, and is then 

 continued towards the upper end. A large pedicellaria is begun with a broad base, a little one with 

 a narrow ba.se. No growth takes place when a coherent margin has been formed all 

 round the valve. — On PI. XII, fig.s. 4 — 5 is .shown a developmental stage of a large tridentate 

 pedicellaria. — I have found such stages of development in most of the sjiecies I have examined. 



Already Duvernoy (op. cit.) and W. B. Herapath^) lay stress upon the fact that the pedi- 



') Memoire sur 1' analogic de composition et sur tiuelques points de 1' organisation des Echinodennes. Mem. de I'lnst. 

 de France. XX. 1849. p. 611. 



2) On the Pedicellariffi of the Echinodermata. Quart Joiini. niicr. Sc. (N. S.) V. 1S65. p. 175— 84. Pis. IV— \^ 



