PRESIDENTIAL ADDRESS. 69 



There are several series of tentacles which when out- 

 stretched have a spread of nearly two inches. 



From the side of the pool, blossoms another and very 

 attractive annelid, Spirographis australiensis. In expan- 

 sion the branchial whorls of this resemble a full head of 

 thistle-down, but at the least alarm the shy creature folds 

 up and sinks down a large membranous tube. An unex- 

 pected tenant of the rock pool is the sea spider, Desis 

 marina, which constructs a diving bell of silk to contain a 

 sufficient supply of air, and so lives in a rock crevice 

 between tide-marks. This is one of the few animals on 

 our beach that can be called retrograde, in the sense of 

 having migrated from land to sea. 



Underlying the zone of Galeolaria is that of Cynthia, 

 another master organism. This association is less extensive 

 only in the line of constant foam does it flourish, and where 

 the surf ceases to beat upon the shore, there Cynthia dis- 

 appears. Downwards it extends into the dwarf-kelp zone, 

 and above it contends with Galeolaria for the possession 

 of a borderland which each may alternately occupy. 



Probably this giant ascidian, Cynthia prceputialis* (fig. 

 36), is an element in our fauna of southern origin. Indeed 

 it seems to be a generalisation of some magnitude, that the 

 organisms of the surf are chiefly Peronian while those of 

 the estuary have a Solanderian tone. 2 The individual tuni- 

 cates form columns about six inches high and two broad, 

 their thick tough husks are grey in colour, and usually are 

 hidden by a growth of algae. On the cupped summit is a 

 double cone of the inhalent and exhalent orifices, which, 

 opening under water, form a crimson cross, and from which 

 above water little jets squirt. Sometimes individuals grow 

 apart, but ordinarily they are so densely packed together 



1 Herdman, Descrip. Cat. Tunicata, Austr. Mus., 1899, p. 27. 

 8 Hedley, Proc. Linn. Soc. N.S. Wales, xxviii, 1903 (1904), p. 880. 



