On a Pair of Ciliated Grooves in the Brain of the Ammoccete. 485 



conductivity has been found to be the same as that of their electrical 

 conductivity. 



As regards the magnetic permeability of these alloys, the order is very 

 different from that of their electric conductivity. The most highly 

 permeable alloys are those formed of aluminium and silicon with iron. 

 In fact, the magnetic permeability of an alloy of iron with 2\ per cent, 

 of silicon exceeds that of the best and purest annealed iron up to a 

 field of 10 C.G.S. units. Still more remarkable is a pure and well 

 annealed alloy of aluminium and iron ; although it contains a con- 

 siderable percentage of non-magnetic elements, its magnetic perme- 

 ability and maximum induction up to a field of 60 units exceeds the 

 best and purest annealed iron that I can obtain, a specimen of Swedish 

 charcoal iron containing 99*9 per cent, of iron, all the specimens 

 having been subjected to a precisely similar annealing process. 



It is possible the increased magnetic susceptibility given to iron by 

 aluminium, and to a less extent by silicon, may be due to the strong 

 chemical affinity which these elements have for oxygen, whereby any 

 of this gas which might be dissociated in the molten iron would be 

 removed, and the texture of the metal thus rendered closer and more 

 uniform. In the same way, by combining with the oxygen, they 

 would remove, as my colleague Professor Hartley suggests, traces of 

 oxide of iron, more or less diffused through all iron ; and the presence 

 of which would certainly lower the magnetic susceptibility. 



The remarkable magnetic properties of these two alloys, especially 

 of the aluminium-iron alloy, is a matter not only of considerable 

 theoretic interest but obviously is also of great practical importance 

 in electrical engineering. 



" On a Pair of Ciliated Grooves in the Brain of the Aminoccvte 

 apparently serving to promote the Circulation of the Fluid 

 in the Brain-cavity." By AUTHUK DEXDY, D.Sc., F.L.S., 

 Professor of Biology in the Canterbury College, University of 

 New Zealand. Communicated by Professor G. B. HOWES, 

 LL.D., F.PuS. Pteceived February 7, Kead February 20, 

 1902. 



The peculiar and apparently hitherto undescribed structures which 

 form the subject of the present communication, were first discovered 

 in the course of an as yet unfinished investigation of the parietal 

 organs in the New Zealand Lamprey (Geotrui australis). The Ammoca-te 

 of this interesting species is known to us only through two specimens : 



2 M 2 



