GENEEA OF THE ALCTONAEIA STOLONIFEEA. 339 



I am convinced, from an examination of a large number of specimens of Alcyonarians, 

 that the number of the zooxanthellae in the coelenteron cannot be used for purposes 

 of classification, since polypes of the same species, and even of the same colony, show 

 very great variation in this respect. Generally speaking, shallow-water polypes possess 

 more than those that live in deeper water, the zooxanthella; being probably dependent 

 for their growth and multiplication upon the intensity of the daylight. But whether 

 this is the only cause or not does not seem certain. At any rate we can say that it is 

 highly probable that the conditions favourable for the growth and multiplication of 

 the zooxanthellee are not precisely the same as those favourable for the growth and 

 multiplication of the Alcyonarian colonies, and thus the variations in the number of 

 these symbiotic algse in the polypes may be accounted for. 



Specimen 2. The stolon is somewhat thicker in the central part of its area than in 

 Specimen 1. It is membranous, but becomes divided at the edges into broad and 

 narrow strands. The polypes are densely crowded on the central parts of the stolon, 

 but scattered at the edges. 



The polypes are partially retracted, but not to such an extent as in Specimen 1, the 

 adpressed tentacles remaining visible in more than fifty per cent, of the polypes. 



The average height of the partially retracted polypes is 3 mm., and their diameter 

 1'5 mm. 



The walls of the polypes are thicker than they are in the first specimen, with dark 

 brown corrugated outer surfaces. 



Spicules resemble those in Specimen 1, but the tubercles are slightly longer and less 

 numerous. Average length 0"15 mm. (Plate L. fig. 6). 



The colony is parastic on a piece of sponge. 



Clavulaeia austealiensis. Variety B. (Plate L. fig. 7.) 



The three specimens that I have grouped together as Variety B of this species are 

 distinguished from the others by the absence of spicules. This fact in itself might be 

 considered by some naturalists to be sufficient reason for the establishment of a new 

 species, or even a new genus, for their reception ; but after a careful examination of the 

 anatomy of the specimens, their mode of growth, structure of the tentacles, and 

 general anatomy, I am convinced that we are not justified in separating into difierent 

 species those forms that differ mainly in the presence or absence of spicules. I believe 

 that it is quite possible that in some localities, where there is but little lime in 

 the water and an abundance of sand, the Clavularias do not develop spicules. This 

 is sufficient to constitute a separate local variety, but not a species. 



Associated with the absence of spicules in this variety there may be noticed a 

 difi'erence in the character of the ectoderm from that of Variety A (Plate L. fig. 8). 



The ectoderm of Variety A is over the great part of ts surface smooth and columnar, 

 each cell being marked ofi" from its neighbours by very definite cell-outlines. In 



