NOTES ON ECHINODERM MORPHOLOGY. 303 



Notes on Echinoderm Morphology, No. XI. On 

 the Development of the Apical Plates in 

 Amphiura squamata. 



By 



P. Herbert Carpenter, D.Sc., F.R.S., F.I/.S., 



Assistant Master at Eton College. 



Some very important observations " On the Development of 

 the Calcareous Plates of Amphiura" have been recently pub- 

 lished by Dr. J. W. Fewkes, 1 who has also eutered into a dis- 

 cussion respecting the morphological relations of these plates. 

 Amphiura squamata is viviparous, and the young undergo 

 a direct or abbreviated development without passing through a 

 definite Pluteus form, so that it is easy to follow the various 

 larval stages and to study the mode of appearance of the 

 skeletal plates. 



Ludwig took up the subject in 1881, 2 and made the very 

 striking discovery that two rings of radially situated plates are 

 developed around the dorsocentral. Those of the distal ring 

 are carried outwards from the disc at the ends of the srrowinsr 

 arms, and are known as the terminals (fig. i, t) ; while the 

 five plates of the proximal ring (4) remain on the disc close to 

 the dorsocentral (1), and with it develop into the rosette of six 

 primary plates which is a prominent feature on the abactina. 

 surface of many adult Ophiurids. In Amphiura squamata 

 two more rings of plates, the intermediate plates of Ludwig, 

 eventually appear between these radials and the dorsocentral ; 



1 'Bull. Mus. Comp. Zool.,' 1887, vol. xiii, No. 4, pp. 107—150, pi. i— iii. 



2 " Zur Entwicklungsgeschichte des Ophiurenskelettes," ' Zeitscbr. f. wiss. 

 Zool.,' 1SS1, Bd. xxsvi, pp. 181—200, Taf. x, xi. 



