rOLYZOA OF WATBRWORKJ'. 435 



oi'ga.msms for a long perio.l, and then to have become suddenly 

 infected. It is at least theoretically possible that Polyzoa are 

 absent in certain waterworks merely because no statoblast or 

 embryo happens to have found access to the system ; even though 

 there may be nothing to prevent these organisms from flourishing 

 if they succeed in ettectiug an entrance. The means of distribu- 

 tion of freshwater organisms have frequently been discussed. 

 Darwin gives important information on the subject in ' The 

 Origin of Species ', Oh. xiii : — vvitli particular reference to dis- 

 persal by water-birds and insects. Other facts of the same 

 nature are recorded by H. Wallis Kew, in ' The Dispersal of 

 Shells' (Internat. Sci. Series, 1893). A short general discussion 

 of the subject was contributed by 0. Zacharias to the ' Biologisshes 

 Centralblatt,' ix. Nos. 3 and 4, April 1889. Reference may also 

 be made to B. M. Puschkarew's recent paper, " Ueber die Ver- 

 breitung der Siisswasserprotozoen durch die Luft" (Arch. f. Pro- 

 tisfcenkunde, xxviii. Heft 3, 1913, p. 323). 



It can hardly be doubted that the method by which Polyzoa 

 most commonly colonize a new place is by means of their stato- 

 blasts, which from their habit of floating at the surface are 

 extremely likely to adhere to some part of the legs, beak, or 

 feathers of a waduig or swimming bird, or to some part of a 

 water-insect. De Guerne (88), struck by the occurrence in the 

 Azores of a lacustrine fauna almost entirely composed of European 

 types, was led to examine the material adhering to the feet of 

 Ducks; and on one occasion (p. 297) he discovered a half stato- 

 blast of a Plumatella on the web of the foot of a Wild Duck. 

 Similar positive information with regard to the dispersal of fresh- 

 water Polyzoa has been published by Garbini, in a paper which I 

 have only been able to consult by means of the notices given in 

 Yol. ii. (p. 195) of the ' Zoologisches Centralblatt', and (by Matz- 

 dorff) in the " Jahresbericht iiber die Bryozoen fiir 1897 und 

 1898 "in the ' Archiv fiir Naturgeschichte,' Ixi. Jahrg., ii. Bd. 

 Heft 3, p. 181. It appears from the latter notice that stato- 

 blasts of a Plamatella were found attached to the beak of a 

 Heron ("Reiher"). 



II. Occurrence of Polyzoa in British Waterworks. 



I turn now to the consideration of the cases which have come 

 under my own observation in this country. I am able to record 

 five cases, in very different parts of Great Britain, in all of which 

 serious trouble has been experienced. I commence by giving 

 some account of the occurrence of the organisms, reserving the 

 question of the determination of the specimens to Part III. of 

 this paper. The cases are as follows : — 



(1) Torquay and jSTewton Abbot. 



Towards tlie end of September 1910, I received samples of a 

 Flumatella {P. emarginata, var. mibscosa) from Mr. »Samuel 

 Proc. ZooL. Soa~1913, No. XXX. 30 



