976 ON SPONGES TN WATERWORKS. 



On visiting the " Heath " and Llanishen on February 3rd, 1912, 

 when the filter-beds were covered with ice 1 1 ins. thick, we found 

 that the adult growth was dying down, but that it was still 

 closely packed with gemmules, some oB which had begun to 

 germinate and start new growths among the old. On March 23rd 

 gemmation had proceeded further, new growths being abundant, 

 and I suggested that in the course of the spring the pipes and 

 chambers should be scraped and treated with strong bi-ine, so 

 applied as to reach any small spaces and crevices in which 

 gemmules could lodge, and thus to attack the sponge when it was 

 least capable of resistance. This was done on May 2nd, and 

 with the sponge were removed a large quantity of iron corrosive 

 nodules— another trial to the Water Engineer, referred to by 

 Harmer on pp. 430, 437, & 438 of his paper ; the brine was then 

 washed out through a bye-pass. The result was apparently satis- 

 factory, but in the course of the summer a few small new growths 

 were observed by the Foreman : they were very much less 

 abundant than in the previous summer, and no smell had been 

 noticed since the treatment. An examination on September 24th 

 showed that these comparatively few young incrusting sponges 

 had not yet given rise to any outgrowths, and that they con- 

 tained no gemmules : they were in all probability due to a few 

 gemmules which had not germinated when the treatment was 

 carried out. I therefore suggested a second application of brine. 

 By November 14th, when this was done, the growths had 

 increased in size considerably, but apparently no gemmules had 

 been formed. Instead of leaving the pipes empty for only a few 

 hours, as on the previous occasion, it was possible this time to 

 give them three days before being again used, and since then no 

 trace of the sponge has been seen. 



It is interesting to note that no Polyzoa were found, but that 

 a number of colourless Hydrje like those described by Kiaepelin 

 at Hamburg were obtained by the reservoir-keeper from the 

 bottom of the valve-shaft at Llanishen on May 25th ; unfor- 

 tunately these were all dead by the time they reached me *. 



* Since the above was written, a few younp: sponge-f^rowths were again observed 

 and at once destroyed. Colonies of Cristatella, with numerous stRtoblasts, had 

 also appeared : fortunately this is not one of the " moss "-forming Polyzoa. (Oct. 

 25th, 1913.) 



