544 DK. S. J. HICKSON — EEVISION OP THE 



The length of the polypes varies according to the size of the colony and the mode 

 of growth. The longest tube I have measured is four inches, but the average length 

 is not more than one or two inches. 



When the tide goes down the crown and neck of the polypes are slowly but 

 completely retracted within the firm walls of the lower part of the polype-tubes. In 

 this firmly retracted condition they retain a considerable quantity of sea-water in their 

 coelentera, and they are able, in consequence, to withstand exposure to the air and sun 

 for an hour or two. 



The stolon consists of a network of tubes and strands clinging to the supporting 

 coral blocks. In some places these strands are somewhat expanded, but I have never 

 found any very extensive membranous plates in this species. 



There are no spicules in the tentacles nor in the crown and neck, but in the lower 

 parts of the body-walls of the polypes there are a few very large calcareous spicules. 

 They are long spindles beset with numerous small spines and tubercles. Their average 

 size is 2-3 mm. long by 0"14 mm. broad (Plate L. fig. 16). 



A series of sections through the polypes shows that the muscular ridges on the 

 mesenteries are very numerous and long (fig. 17) ; in fact the mesenterial muscles of 

 Clavularia viridis are stronger than any I have met with in the Alcyonaria, excepting 

 perhaps Tubipora (9). 



The mesogloea is very thick for a Stoloniferan, both in the tentacles and body-wall. 



The spicules are situated in the mesogloea, and in transverse sections of decalcified 

 specimens empty spaces may be seen, indicating the places that they formerly occupied. 



The horny skeleton is formed by some modification of the mesogloea. It occurs in 

 the form of a number of very dense fibres, which are figured in transverse sections in 

 Plate L. fig. 18 h.f. They appear in the form of deeply stained cores situated in the 

 centres of wide lacuns; in the homogeneous mesogloea. 



It is difiicult to determine the exact chemical nature of this horny skeleton, but it 

 is apparently closely related to keratin. 



It is insoluble in weak and strong nitric and hydrochloric acid. It is partially 

 soluble in strong hot sulphuric acid. It is not digested by pepsin and "2 per cent, 

 hydrochloric acid, nor by solution of pancreatin. 



On burning it gives a pungent and somewhat aromatic odour. 



In origin it differs from the horny skeleton of Cornularia and Stereosoma in being 

 a product of the mesogloea. There is nothing that resembles it in any other species 

 of the senus. 



&^ 



List of the Literature referred to. 



I. DE Blainville. — Manuel d'Actinologie. 



2. DELLE Chiaje. — Descriz. e anotom. degh Anim. inv. della Sicilia Citer. t. v. p. 160, fig. 5. 



3. Dana, J. D. — United States Exploring Expedition. Zoophytes. 1848. 



