190 Transactions. 



The radium-emanation content of the water taken actually from the 

 well-pipe was in this case 135-5. These numbers show very conclusively 

 how marked is the diminution of mortality with recession from the well ; 

 and, put another way, there is a strong correspondence between the number 

 of dead eggs and the radium emanation. Thus, taking on the one hand the 

 number of dead eggs in the top box as 100 x {x, of course, then equals 66-7) 

 and the radium-emanation content of the top box as 100^ (then y is l-z6), 

 we have the following correspondences : — 



First pair of boxes 

 Second ., 



Third „ 



Fourth „ 



Fifth 



It is only right to add that these tigures do not represent in any way the 

 present practice at the hatchery. It was known that the mortality would 

 be high, though the cause was not known ; and it was to ascertain the 

 cause that so large a number of eggs were sacrificed. 



The figures with regard to blue swelling as it subsequently developed 

 in these boxes, and to gas content, are given in the paper dealing with the 

 dissolved gases {loc. cit.) ; but, even if death in maturer fish can be ascribed 

 to an excess of gas, which to us does not yet appear to be certain, it is 

 difficult to apply the theory of Marsh and Goreham to the mortality in 

 eggs or to blue swelhng. 



Art. XVI. — On an Isopod inhabiting Ants'' Nests in New Zealand. 

 By Charles Chilton, M.A., D.Sc, F.L.S. 



[Bead before the Philosophical Institute of Canterbury, 3rd November, 1C09.] 



It has long been known that an isopod, Plaiyarthrus hoffmannseggii, Brandt, 

 is found associated with several species of ants in England and Europe. 

 It has been described by Bate and Westwood,* Schoebl,| Webb and Sillem,{ 

 and others. Lord Avebury§ has also published the result of his observa- 

 tions and experiments upon it. and has suggested that it ac;J;s as a scavenger 

 in the ants' nest. 



AVhen I was preparing my paper on the terrestrial Isopoda of New 

 Zealand! I in 1900, I heard from Mr. W. W. Smith that he had found two 

 specimens of an isopod supposed to belong to the genus Platyarthrus in 

 ants' nests in New Zealand, and that these had been forwarded along -^dth 

 the ants to specialists in Europe. My efltorts to trace these specimens were 



* " British Sessile-eyed CVnstacea," 11, p. 464. 



fSitzungsb. d. k. Akad. d. W. math, natm-w. CI. xl Bd.. Xo. 9, I860, p. 279. 



i " The British Woodlice." 1906, p. 30. 



§ " Ants, Bees, and Wasjis." 16th edition, 1^02. pp. 75. 90. and 407. 



II Trans. Liim. Soc, 2nd ser., Zool., vol. viii, p. 100. 



