726 DR. W. B. CARPENTER ON THE STRUCTURE, PHYSIOLOGY, AND 



v.— DEVELOPMENT OF THE SKELETON. 



1. General History of the Pentacrinoid Larva. 



67. The study of the development of the pieces of which the Skeleton of Antedon is 

 made up, will be best pursued in the first instance by following the general history of the 

 development of its Pentacrinoid Larva, from the epoch at which Professor Wyville 

 Thomson's account of it ceases, to the termination of its attached condition ; since it will 

 be in this mode that I can best make apparent the relation of the remarkable changes 

 which the skeleton undergoes during this period, to the progressive evolution of the 

 other parts of the fabric. 



58. The nature of the objects to which the Pentacrinoid Larvae attach themselves, 

 varies with the locality. In Lamlash Bay, Arran, where my own studies oi Antedon have 

 been for the most part carried on, I have never found them affixed to anything else than 

 the fronds of Laminarice (to which the adult Antedon habitually clings), or to Polyzoa 

 or Spirorbes attached to these. But at Ilfracombe, where Laminarice are much less 

 abundant, but where the Polyzoon Salicornaria grows in great luxuriance in the habitat 

 of Antedon, the Pentacrinoid larvae are found adherent to its stony Polyzoary. Mr. J. V. 

 Thompsok found them in the Bay of Cork " attached to the various species of Sertu- 

 laria and Flustracea which occur in the deeper parts of the harbour of Cove, viz. in from 

 eight to ten fathoms." Mr. William Thompson (of Belfast) found them attached to 

 Delesseria sanguinea. Hence I think it can scarcely be doubted that the Pentacrinoids 

 will attach themselves indifferently to any Fuci, Polyparies, or Polyzoaries, which 

 may abound in the habitats of the parent Antedon. Though generally scattered over 

 the surfaces of these, so as not to be in any near proximity to each other, yet sometimes 

 we meet with a group of several Pentacrinoids very close together, so as to present in one 

 view all the stages in development represented in Plate XXXIX. I have one specimen 

 in my possession, indeed, in which moi'e than seventy Pentacrinoids, all nearly in the 

 same stage of development, are attached to the surface of a patch of Metnbranipora that 

 was encrusting a frond of Laminaria ; and in another, which I owe to the kindness of 

 Professor Wyville Thomson, thirty-five Pentacrinoids, in that earlier stage which was 

 first described by Professor Allman, are so closely clustered together that the discoidal 

 bases of their stems have come into mutual contact, and have acquired a polygonal 

 form. These, he informs me, were bred in his Vivarium; and the circumstances of 

 their aggregation were not a little curious. A pseudembryo, when losing its power of 

 locomotion, was frequently seen floating in such a manner that its incipient discoidal base 

 spread itself out (often in a stellate form) on the surface of the water, whilst the stem, 

 and body of the rudimental Pentacrinoid hung dowTiwards from this ; and it sometimes 

 happened that by the approximation of a number of individuals in the same condition, 

 the stellate extensions of the disks became mutually adherent. Similar clusters were 

 found by Professor Wyville Thomson attached to the inner surface of a dead valve of 

 Modiola modiolus. 



