218 Proceedings of the Royal Irish Academy. 



the same places in July, 1916, resulted in the finding of a very few small 

 specimens, in the course of three days' search, on the metamorphic rocks in 

 the lake, while none was seen on tlie limestone. In the tropics, where 

 gemmules are produced in stich abundance at the approach of the dry season, 

 a fresh growth of sponges is ensured when the water again reaches its winter 

 level. With the occasional exceptions of Ejihydatia fluviatUis, and in a less 

 degree Spovrplla lacus/ns, gemmules are not abundant in lake sponges in 

 Ireland, so that there is not much cliance of sponges which are left higli and 

 dry during an unusually rainles.s summer being reproduced in situ by their 

 means. In this connexion it may be stated that, on the whole, gemmules are 

 not produced in very great numbers by fresh-water sponges in Ireland, no 

 doubt owing to the temperate climate. The river form of Htfrroviti/cnia 

 Ryderi, and sometimes Ephijdatva flumatilis, may give rise to a certain 

 abundance of gemmules, but I have seen notliing in Irish speciinens at all 

 comparal)le to llie ma.sses of gemmules produced by sponges in the tropics. 

 Dr. Annandale, who lias such an extensive knowledge of the tropical 

 Spongillidae, comnicntfi on the scarcity of gemmules in a collection of sponges 

 from France and Switzprlaml examined by him (4, p. 393). His remark 

 wouM aji]>ly jiorhnps oven more forcibly to Irish specimens. Although not 

 jiroducod in extraordinary number.'^, gemmides may be found apj)arenlly at 

 alraast any time of the year. Again, owing to our temperate climate, there 

 would appear to bo no particular need to produce them at any special season. 

 They are. however, more abundant on the whole in llic late summer and 

 auliimn. 



I liave never found sponges along the shores of lakes, such as Crotty's 

 Ix>ugh in the Comeragh MounUiins, or L«iugli Shimnagh in the Mourne 

 MounUins, that arc used as a water-supply for neighbouring towns and 

 cities. This is, perhaps, to l>e accounted for by tiie rapid and frequent 

 changes in the water-level in these lakes. 



Sponges were not found in any of the lakes in the Mourne Mountains, 

 although, apart from Lough Shimnagh, the lakes appeared suited to their 

 growth. Sponges occur in such abundance and with such regularity in 

 mounUin tarns throughout Ireland that their apparent total absence from 

 the Mournes i.s noteworthy. 



The jKoition in which sponges grow with the greatest luxuriance in this 

 country is in a stream or river wliich drains a lake, and at a point a greater or 

 less distance Itelow the lake. This applies both to small mountain streams, 

 as already described (p. 217), and to the large lowland rivers. Ffir example, 

 aljout half a mile l>elow Ixuigh Allen the pebbly l>ed of the River Shannon 

 waa found to b.- iitvially < irpc-U'd with growths of Sixnyjilln lacmtris. For 



