ALCYONIID^E. 25!) 



ANATOMICAL NOTES.* 

 Nematocysts (tigs. 13 and 14). 



Moseley was unable to find nematocysts in specimens of Sarcophytum, and there- 

 fore states (1881, p. L19) that they do not occur in this genus. In his description 

 of the occurrence of nematocysts in several members of the Alcyonaria, Ash worth 

 (1899, p. L93) records them for Sarcophytum pauciflorum. This species, however, 

 is now placed in the genus Lobophytum, for which the record of the presence of 

 nematocysts is new. Hitherto they have not heen observed in any species of 

 Sarcophytum. 



On examining several preparations of a single species stained with iron hrazilin, 

 some specimens seemed to contain no nematocysts, many contained few nematocysts, 

 and in only a very few instances were they at all numerous. The apparent absence 

 or scarcity of nematocysts in individual memhers of a species may be attributed to 

 the use of a fixing preservative which permeates the tissues so slowly that the 

 stinging cells are discharged before the colony is fixed. If a rapidly fixing preserva- 

 tive such as an 8 per cent, aqueous solution of hot formalin he employed, the tissues 

 apparently suffer no contraction and the tentacles are found to contain innumerable 

 batteries of nematocysts. 



Nematocysts in Alcyonium digitatum were first described by Htckson (1895). 



I have been successful in observing nematocysts in all the species of Alcyonium, 

 Sarcophytum, Lobophytum, and Sclerophytum which I have examined. They are, 

 however, apparently more numerous in the British species than in the tropical 

 representatives of the family. They always occur in batteries, and are never 

 uniformly distributed in the ectoderm. The most common type is the well-known 

 form occurring in Alcyonium. Modifications of this with regard to size, and length 

 and thickness of thread are not infrequent, and may be found in Sarcophytum roseum 

 (fig. 13) and S. glaucum (fig. 13c), and in Sclerophytum gardineri-. The accompanying- 

 table shows that they vary considerably in size in specific members of the family, and 

 are apparently more uniform in this respect in Alcyonium and Lobophytum than in 

 Sarcophytum, where they are from 6/jl to '1'Ijj. long, and from 2/x to 14/a broad, and 

 in Sclerophytum, in which they are from 5/x to 12/jl long, and from 2(i to 4ya broad. 



Nematocysts attain their greatest size in Sarcophytum glaucum (fig. 13c), in which 

 species they are comparatively few in number. The thread is extremely short and 

 broad, being usually fully 2/x in breadth. In sections, the internal portion exposed 

 at the cut surface stains more deeply than the external portion of the thread. 

 Within the cell the thread lies loosely and irregularly coiled, there being usually only 

 from 3 to 4 turns of the spiral. The smallest nematocysts occur in Sclerophytum 



* I have given an account of the physiology and comparative anatomy of the digestive organs of the 

 Alcyonaria in a paper which is in the Press at the time of writing (Pratt, 1905). 



2L2 



