December. 1910. 



KNOWLEDGE. 



487 



discovered is a fine sie\e covering the so-called eye-spot in 

 Cosciiiodiscits asteromphalus. As the size of the eye-spot 

 is only ti^tju of an inch, it may be left to the imagination to 

 estimate the size of the minute perforations forming the sieve. 

 There was an exhibition of Pond-life by Fellows of the Society, 

 assisted by Members of the Quekett Nlicroscopical Club. 



QUEKETT MICROSCOPICAL CLUB.— October 25th. 

 igfo. Prof. E. A. Minchin. M.A.. F.Z.S.. President, in the 

 chair. .\ paper on " Some new African species of Volvox " by 

 Prof. G. S. West, M.A., D.Sc, F.L.S., was communicated by 

 Mr. C. F. Rousselet. The first part of the paper referred to 

 the two European species V. globator and V. aureus, both 

 very well known and with clearly established specific 

 characters. .\ synopsis of the distinctive characters of these 

 two species was given. Reference \\a; niadt- to the doubtful 

 third European species 

 V. tertius. A. Meyer. 1S96. 

 and to the description by 

 J. H. Powers of several new 

 American forms, 1905-1906. 

 The two new species now re- 

 corded are Volvox rousscleti 

 from Rhodesia, and V. 

 africaitus from the .Albert 

 Nyanza. 



Mr. .A. Earland communi- 

 cated a paper by Mr. H. Side- 

 bottom on ■■ Two new species 

 of CassiduliiuT." These were 

 Cassiduliua clcgaits and C. 

 decorata. both obtained by 

 H.M.S. Waterwitch at 

 station 159 S.W. Pacific, depth 

 1050 fathoms. The second 

 form was also found at station 

 256, 505 fathoms. 



Mr. C. D. Soar. F.R.M.S., 

 read "A Contribution to the 

 list of Hydrachnidae found in 

 the East .African Lakes." The 

 material examined was from 

 the Victoria Nyanza, L. 

 Tanganyika and L. Nyassa. 

 The \'ictoria Nyanza tube 

 (yielded only one species FiGL'RE 3. .A Colony of Ciis 

 (U n ion icul a Jigural is, Koch.) 



which it was possible to identify. From Lake Tanganyika six 

 species were noted, of which three are new to science. These 

 are Neuniaiiia papulosa. Mideopsis niittuta and 

 Hygrobates cdentipalpis. Tube No. 3, from L. Nyassa. 

 yielded but one species, but this was also new, and is named 

 Unioiiicula cuuniiigtotii : it is vers- close to U. figuralis. 

 Koch, but among other differences has a long spUt seta 

 exactly behind the eyes. The author knew of no other mite 

 having this distinguishing characteristic. 



-AH the new species brought forward were exhibited at this 

 meeting, and are fully described and figured in the November 

 issue of the Journal of the Quekett Microscopical Club. 



Mr. -A. C. Banfield exhibited living specimens of Cristatella 

 niucedo, abnormally hatched out from statoblasts about four 

 months before the usual time. 



PHOTOMICROGRAPHY.— We havereceived from Messrs. 

 Wratten & Wainwright. Ltd.. Croydon, a small booklet under 

 the above title, which deals in a simple and clear manner with 

 some of the practical difficulties found by beginners. -As the 

 object of taking photomicrographs is to exhibit as clearly as 

 possible the structure of the specimen, the question of contrast 

 is all important. Here the advantages of the use of a suitable 

 screen becomes apparent, and on page 9 a table is given show- 

 ing which screen is most suitable for use with the ordinary- 

 staining media. The booklet, which is well got up, is illustrated 

 with reproductions of several photomicrographs. 



PREMATURE HATCHING OF CRISTATELLA 

 MUCEDO. — During the last week of September I received, 

 through the kindness of Mr. Rousselet, a considerable number 

 of statoblasts of C. niucedo. Except in their most unusual 

 cleanliness there was nothing remarkable in their appearance, 

 and I placed them in a tank to await development. 



I have on many occasions hatched out and bred these 

 beautiful Pol\zoa. this act always taking place at the end of 

 February and early in March. On October 3rd I was hunting 

 other organisms in the same tank, and to my astonishment 

 saw that four of the statoblasts had hatched out, and the 

 tiny zooids were particularly healthy and vigorous. It seems 

 to me remarkable that these four indi\iduals should have 

 hatched out prematurely by no less than five months, and. 

 what is perhaps still more curious, that only four out of 

 the large number I received did hatch out. 



1 can offer no explanation ; 

 it cannot be the effect of tem- 

 perature or more would have 

 hatched. The tank tempera- 

 ture was 5S°F., and the tap 

 water at the same time 55°F. 

 If the difference of 3°F. was 

 enough to influence the ap- 

 pearance of four individuals, 

 why not others r 



The animal during the first 

 few days grows at the rate of 

 a zooid a day, the photo- 

 graph reproduced in Figure 3 

 showing the appearance of a 

 colony three days old. These 

 \ oung colonies are extremely 

 difficult to narcotise and fix : 

 after five hours constant 

 attention the youngest zooid 

 of the colony reproduced in 

 Figure 3 suddenly retracted 

 and refused to be coaxed out 

 again in spite of all my 

 exertions I An adult colony 

 presents no difficulty of this 

 sort. 



I have two colonies that are 



still alive and healthy ; the 



tatclla niucedo. three days old. larger one is now composed of 



nineteen individuals. Although 

 there is plenty of weed in the tank they prefer to float upside 

 down on the surface film of the water. They are now beauti- 

 fully "tame"; constant familiarity with pipette and tweezers 

 has evidently bred contempt, for nothing short of pushing a 

 zooid in with a dissecting needle will cause it to retract. 



.Arthlr C. Banfield. 



PHOTOGR.APHY. 



By C. E. Kenneth Mees. D.Sc. (Lond.), F.C.S. 



COLOURED SILVER IMAGES.— .AH photographers are 

 aware of the coloured or " warm-tone " images which are 

 produced upon slow plates by restrained development, accom- 

 panied by an exposure considerably greater than that required 

 for black tones ; but the cause of these coloured images is 

 not generally understood. That the colour is not body colour 

 is shown at once by the fact that the colour by reflection is 

 quite different, usually complementan-, to that given to the 

 transmitted light. No arrangement or structure in the film is 

 \-isible, so that interference-colours are not possible, while the 

 variety of tones produced would seem to exclude the colours 

 of turbid media. 



In the investigation of the subject by Schaum and 

 Schloemann, these authors came to the conclusion that the 



