195 



are plainly visible : but in about a week all traces of structure, 

 with the occasional exception of the eye-spots, disappear. Mr. 

 Scourfield said it had been suggested that the "simplex forms" 

 of Richters were these encysted individuals redeveloping their 

 organs. With regard to the position of the Tardigrades in 

 systematic classification, they were usually placed in the Arach- 

 nida close to the Mites, but the segmentation of the appendages 

 is very weakly developed, the pharynx is strikingly like what 

 occurs in some worms, such as Nematodes, and there are no traces 

 of a tracheal system. 



After some discussion of the paper, Mr. D. J. Scourfield, F.Z.S., 

 F.R.M.S., read a paper on " An Alona and a Pleuroxus new to 

 Britain." The first described was Alona ireltaeri, Keilhack. The 

 specimen had been taken as long ago as 1895 by Dr. T. Scott, in 

 a little pool on the Castle Jhll at Scarborough, but had never 

 been recorded. It is closely allied to the fairly common Alona 

 costata, but the post-abdomen is quite characteristic. The second, 

 Plenro.i'us denticulatns, Birge, Mr. Scourfield had obtained on 

 August 30th, 1905, from a small pond close to the railway station 

 at Exminster, Devonshire. It is a typically American species, 

 and apparently has not been previously recorded on this side of 

 the Atlantic. It may therefore have been recently introduced, 

 and it will be interesting to know whether it succeeds in estab- 

 lishing itself in this country. 



At the meeting of the Club held on April 19th, 1907, Dr. 

 G. C. Karop, F.R.M.S., Vice-President, in the Chair, the minutes 

 of the meeting held on March 15th w r ere read and confirmed. 



Messrs. F. R. T. Lucas, Alfred J. Pownall, T. A. Ford, and 

 C. W. Littlejohn were balloted for and duly elected members of 

 the Club. 



Mr. Conrad Beck gave a demonstration on the comparison of 

 objectives, and illustrated his remarks by a number of microscopes 

 arranged to show the apparatus and methods usually employed 

 for that purpose. Members were reminded that objectives can 

 only be properly compared when their distinguishing charac- 

 teristics are known. For the microscopist only two things are 

 required to be known: (1) the magnifying power, (2) the aper- 

 ture. Various methods of measuring the magnifying power were 

 shown — from a simple method suitable for use with low powers 



