REPORT ON THE HOLOTHURIOIDEA. 125 



I examined the very minute pedicels in some very young individuals of Oneirophanta, 

 which pedicels were evidently in an early state of evolution. The extremely thin walls 

 of the pedicels contained only a few small, simple spicules, which, more or less developed, 

 were always surrounded by an evident sheath, and this when treated with hsematoxylin 

 became deeply coloured and very manifest. Supposing the sheaths to be developed 

 first, — the calcareous matters being subsequently produced by them, — I expected to 

 find small empty sheaths, and I succeeded in doing so. The smallest sheath I could 

 discover attained the inconsiderable length of 0"08 mm. (PL XXXVI. fig. 8), and was 

 consequently extremely minute in proportion to the adjacent more developed sheaths, 

 which had a length of about 0'7 mm. The walls of the sheaths are extremely thin 

 and contain scattered cells. I did not discover any epithelial lining, which Semper 1 has 

 observed inside the sheaths in the Synaptidse. As the material which has been at my 

 disposal has not been sufficient to admit any satisfactory examination, it is possible 

 that such an epithelial lining is present though it has escaped my attention. When 

 stained with a solution of hsematoxylin the sheaths become violet, while the structureless 

 matters which they contain remain almost colourless. The sheaths increase and gradually 

 assume the shape of a spicule. I have first discovered calcareous matter inside them 

 when they have attained a length of about 0"20 mm., which, in the shape of a minute, 

 elongate bright body (PI. XXXVI. figs. 10 and 11), is situated in the centre of the 

 hitherto structureless substance ; sometimes two small calcareous bodies are present. 

 At the same time that the carbonate of lime appears, a concentric structure becomes 

 obvious within the substance enclosed by the sheath, which structure is most con- 

 spicuous round the minute recently-formed calcareous body. The sheaths increase, 

 approaching gradually the shape of the future calcareous spicule, while the calcareous 

 deposits themselves grow larger, until they finally become most closely encircled by the 

 wall of the sheaths. It is most probable that a solution of lime-salts is secreted by the 

 walls of the sheaths, and that the calcareous bodies are deposited from this secretion. 



The shape of the calcareous deposits varies at different places in the body. There is, 

 for instance, a certain difference traceable between the deposits of the dorsal surface 

 and those of the ventral one with regard to their shape as well as to their number. The 

 dorsal surface seems regularly to be rougher than the ventral, and consequently the 

 calcareous deposits of the latter surface are often fewer in number, smaller and of a more 

 irregular form, their outwardly-directed processes, which cause the roughness, being short 

 or sometimes altogether wanting. The tentacles, the pedicels, and the dorsal processes 

 are towards their ends strengthened by a greater or smaller number of more or less 

 simple spicules, the shape of which is discussed under the description of the species. The 

 dorsal processes are usually supported by a smaller number of spicules, which seem 

 sometimes to be absent, in which case the walls of the processes are provided with 



1 Reisen im Arohipel der Philippineu, pp. 30, 31, pi. vii. fig. 2, d. 



