Stkpiikns — Tlie Fresh-wafer Sponges of Ireland. 219 



the most part tlie sponge sent iij) hiaiielics from an encrusting base, but 

 unbranched, encrusting specimens were also common. Some miles down UK- 

 river the sponge grew in fairly numerous isolated patches, but in nothing 

 like the abundance in which it ilourished at the first-mentioned point. The 

 western shore of Lough Allen had been examined on the same and previous 

 days, and proved to be almost bare of sponges, a few small specimens of 

 SponrjiUa. lacustria being found in a sheltered bay at the south-western end of 

 the lake. The extreme scarcity .of sponges in the lake thus contrasted 

 strongly with their abundance in the river. Again, in County Sligo, the l«d 

 of the Drumcliff Eiver, a hundred yards or so below Glencar Lough, was 

 covered by a luxuriant growth of the same species, both branching and 

 encrusting specimens again occurring. Glencar Lough itself yielded only a 

 few small specimens. In non-calcareous areas Heteromeycnia Eydcri often 

 grows in out-flowing streams, with stony bottoms, just below a lake both in 

 the mountains and in low-lying localities. As this species grows hidden 

 from the light, the uppermost layer of stones must be removed before the 

 sponge can be seen practically covering the bed of the stream, as well as the 

 lower surfaces of the top layer of stones. 



I have not been able to find any reference in the literature of fresh-water 

 sponges which would show that a similar rule with regard to the growth of 

 sponges has been observed to hold good in other countries — namely, that 

 sponges occur most luxuriantly in a stream or river that drains a lake, and 

 at a spot a little distant below the lake. Edward Potts (30, p. 218) noticed, 

 indeed, that Sponfjilla laciistris was particularly abundant at an outlet from 

 the Fairmount Keservoir, " its stems forming a complete matting over many 

 yards of surface," and Dr. Annandale (6, p. 65, p. 72) remarks of a certain 

 sitecies, J^iulospoiu/illa mappa Annandale, which occurs both in the Lake of 

 Tiberias and in the Eiver Jordan, that the largest specimens were taken from 

 the Jordan near its exit from the lake. These are isolated instances, but 

 they tend to show that the rule, as one w'ould expect, probably holds good in 

 other countries. 



In the course of the Glare Island Survey two dilfei'ences were noticed 

 between the sponges in the lakes of the limestone area examined and those 

 in the lakes lying on non-calcareous rocks (41). First, that sponges were 

 less numerous, and, as a rule, of less luxuriant growth in the lakes on the 

 limestone ; and, secondly, that Hetcromeijaiia Ri/deri was not found in any 

 of the lakes on the limestone, but occurred in abundance in neighbouring 

 lakes on non-calcareous rocks. These two points are further confirmed l)y 

 the field-work since carried out in many other parts of Ireland. 



With regard to the first point, the statement that sponges grow, as a 



