ECHINOIDEA. I. 



stages of the large ones of the same kind. Duvernoy 1 ) even thinks all the different kinds of pedieel- 

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

 writes of the triphyllous pedieellarise: <Je n'ai pu m'assurer si ce sont des pedieellaires d'nne espece 

 particuliere, on s'ils ue sont que le jevme age des pedieellaires ophicephales», and Agassiz, in <Rev. 

 of. Ech. p. 665, says: «in Echinometra there is no doubt these trifoliate pedieellarise are only the 

 younger stages of the tridactyle forms . Scarcely any student of these forms will now-a-days suppose 

 one form of pedicellaria? to be a developmental stage of the other. On the other hand it must be 

 admitted that at a first glance the small pedieellarise 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! Pedieellarise 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. Doderleiu (116) 

 has seen and figured such half-formed pedieellarise of Stcrcocidaris grandis and «Lciocidaris' vcrticillata, 

 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 geseheu habe, die sich auf 

 Praparaten ganz vereinzelt neben den auderen Formen fanden. Diese < korbformigen Klappen zeigen 

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

 Of fining 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 aussere Gestalt der dick- 

 kopfigeu Form, sie sind dagegeu sehr klein bei L. verticillata; bei anderen Arten kenne ich sie nicht, 

 audi ihren Standort konnte ich nicht eutdecken (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 Phormosoma placenta 

 possessing such structures in large numbers and in different sizes, and then there was 110 doubt that 

 they are developmental stages of pedieellarise. On PL 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 valve. -- On PL 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 2 ) lay stress upon the fact that the pedi- 



') Mernoire sur l'analogie de composition et sur quelques points de 1' organisation des Echinodennes. Mem. de l'lust. 

 de France. XX. 1849. P- 611. 



-1 On the Pedicellariae of the Echinodermata. Quart. Journ. micr. Sc. IN. S.) V. 1S65. p. 175— S4. Pis. IV— V. 



