ECHINOIDEA. I. 



stages of the large oiies of the same kind. Diivernoy') eveii thinks all the different kinds of pedicel- 

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

 writes of the tripli5'llons pedicellariæ: <:Je n'ai pn m'assnrer si ce sont des pédicellaires d'une e.spéce 

 particuliére, ou s'ils ne sont qne le jeune åge des pédicellaires ophicephales», and Agassiz, in Rev. 

 of. Ech.s p. 665, savs: <:in Echinometra there is no donbt these trifoliate pedicellariæ are only the 

 younger stages of the tridactyle forms». Scarcel\- any student of these forms will no\v-a-days suppose 

 oue form of pedicellariæ to be a developmental stage of the other. On the other hånd it must be 

 admitted that at a first glance the small pedicellariæ 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! — Pedicellariæ 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 pedicellariæ of Sfcrcocidaris grandis and '.■Lciocidaris-, verticillata^ 

 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 håbe, die sich auf 

 Pråparaten ganz vereinzelt neben den anderen Formen fanden. Diese <korbformigen>> Klappen zeigen 

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

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

 handen. Solche Pedicellarien erreichen bei C. graudis die Grosse und die aussere Gestalt der dick- 

 kopfigen Form, sie sind dagegen sehr klein bei L. Tcrticillafa; bei anderen Arten kenne ich sie nicht, 

 auch 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 sonie specimens of PJwrmosoiiia placenta 

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

 they are developmental stages of pedicellariæ. 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 contemporaneously. From the basal part then the blade 

 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 base. No growth takes place when a coherent margin has been formed all 

 round the val ve. — On PI. XII, figs. 4—5 is shown a developmental stage of a large tridentate 

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



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



I) Mémoire sur l'analogie de composition et sur quelques points de l'organisation des Echiuodermes. Mém. de l'Iust. 

 de France. XX. 1849. P- ^ii. 



-) On the Pedicellariæ of the Echinodermata. Quart. Journ. mier. Se. (N. S.) V. 1S65. p. 175— 84. Pis. IV— V. 



