486 



KNOWLEDGE. 



December, 1910. 



mastax sets up a pumping action wliich sucks up the soft 

 parts of the victim. 



The accompanying ilkistration shows such a scene and double 

 tragedy, which I witnessed, but which I stopped by killing and 

 mounting all the dramatis personae in the middle of the 

 performance. The anterior individual is being carried in the 

 jaws of its captor, whilst the latter has been caught a moment 

 later by a third Plocsonm, intent on devouring both. On 

 looking at this picture one can almost imagine hearing the first 

 victim's desperate call of "Help. Murder!" and a moment 

 afterwards the second's yell : " Oh I let go, yon \illain." 



.Another, but more unlikeh-. interpretation of the situation is 

 the suggestion that the third Ploesoma may be a friend of the 

 first victim, who having witnessed the attack, has come to 

 render assistance in the most effecti\e manner. 



However this may be, the great tragedy in real life appears 

 almost comical to the observer, and I record it here for the 

 information of those interested in Pond Life. My thanks are 

 due to Mr. A. C. Banfield, who has been good Piiough to 

 photograph my slide for the benefit of the readers of 

 " Kxowr.KDGK." 



Charles F. Roussei.i-t, F.R.M.S. 



CRYSTALLIZATION OF SI L VE R.— Of the many 

 interesting examples of crystallization which may be seen 

 under the microscope there is perhaps nothing more fascinat- 

 ing than to watch the growth of crystals of metallic silver as 

 they spread gradually over the field in beautiful fern-like forms, 

 reflecting the light with great brilliancy as it falls upon them 

 from a bull's-eye condenser or a side reflector. These may 

 easily be produced by dissolving some crystals of silver nitrate 

 in distilled water, and putting a little of the solution into a 

 clean copper ring cell, when the growth will at once start from 

 the sides of the cell and gradually extend towards the centre 

 until its entire area is covered. If a glass cell is used, a 

 similar growth may be seen by dropping into the solution a 

 piece of clean copper wire, on which the crystals will at once 

 commence to form. It is not possible to preserve the beauty 

 of the contents of the cells for any length of time, as the new 

 compound formed by the union of the acid with the copper 

 soon clouds the liquid, finally depositing minute crystals of 

 copper nitrate upon the silver and in this way eft'ectually 

 spoiling its lustre. A better way of showing the formation of 

 crystals of silver is by using a rather deeper cell made of 

 gutta-percha, ebonite, or other non-conductor of electricity, 

 through the opposite sides of which two fine platinum wires 

 have been passed so that one end of each projects slightly into 

 the cell. The other ends of these wires should then be coimccted 

 with a battery provided with a means of breaking or reversing 

 the current at will. If now the current be switched on, the 

 growth of metallic silver crystals will be seen to start from the 

 platinum wires and will continue until those from the opposite 

 sides come into contact. If during the process the circuit is 

 broken the growth will instantly cease, whilst if the current is 

 reversed the crystals will disappear in the inverse order of 

 their formation, and the curious effect of ferns iingrowing 

 will be seen. As soon as the last crystal has disappeared a 

 new growth will start, but this time the distinctive forms will 

 be developed from the wires opposite to those whence they 



formerly proceeded. ,, ,_ , 



R. r. Licwis. 



MASS! LI NA SECANS.— In the August number of 

 " Knovvi,edge " an article by Messrs. Heron-Allen and 

 Earland on MassiJina sccaits, invited information as to the 

 prevalence of this species on the East Coast. A holiday at 

 Cromer afforded some opportunity for investigation, and a 

 series of shore-gatherings demonstrated the existence of this 

 form. It may be mentioned that the beach in this district 

 consists of immense stretches of fine sand. Towards the 

 west there appears to be a considerable extent of low-lying 

 rock, the nearer fringe of which is just uncovered at low 

 water. 



Gatherings from the eastward or more open beach produced 

 specimens. They occur somewhat sparsely, and in no case 



was there any indication of the vast accumulations existing oft' 

 the Irish coast and the southern coast of England. Those, 

 howe\er, which were taken are remarkably true to type, 

 porcellanous in texture, with chambers well-marked and 

 symmetrical. An examination of some hundreds revealed 

 little variation in the relative proportions of the chambers, in 

 the shape, or in tint. Compared with those taken from the 

 Irish coast, the specimens gathered from the open beach were, 

 generally speaking, flatter, the chambers being more oval in 

 section, and there was a conspicuous absence of abnormal or 

 eccentric forms. 



The accessible rock-pools, which are \ery inconsiderable in 

 extent in this district, aftorded far more specimens, and these 

 differ considerably from what may be regarded as the type. 

 There is a want of synunetry in the chambers ; in some cases 

 both the outer chambers are of abnormal size, in other cases 

 one only has been developed in this manner. The walls are 

 marked with exterior folds, with striae, and with outgrowths 

 of irregular shape, which apparently indicate successful 

 attempts to repair fracture or damage. 



The chambers are, in many instances, more circular in 

 section and coarser in texture than in the case of those 

 gathered from the open. Nor is the colour uniform, the dull 

 white of the type being marked with blotches of pink, of 

 brown and of greenish yellow, and in one or two cases the 

 specimens assume an almost vitreous appearance. 



These variations, which seem to indicate a highly-developed 

 faculty on the part of the organism to adapt itself to circum- 

 stances, are probably due to the altered conditions of 

 existence in the comparatively restricted area of the rock-pools. 



In any case, the conclusions of the authors of the article 



referred to, that Massilina sccans is an organism of 



abundant vitality, well able to accommodate itself to its 



surroundings, and that the different varieties described by 



earlier authorities on the subject may be more correctly 



described as accidental variations from the type, appear to be 



well founded. ,- , 



I^RED Lewis. 



ROYAL MICROSCOPICAL SOCIETY, October 19th, 

 1910. Mr. E. J. Spitta, L.R.C. P., Vice-President, in the chair. 

 A paper by Mr. Jas. J. Simpson, M.A., B.Sc, on " Hicksoiiclla, 

 a new Gorgonellid Genus," was read. The genus is established 

 to include three species collected off South Africa. One 

 species was described by Prof. Hickson. in 1904, under the 

 name of Juncclla spiralis, but the author showed that a 

 reference to the genus Juncella was impossible. The clearing 

 up of the position of this puzzling specimen was facilitated by 

 recent work of the author in his revision of the family of the 

 Juncellids. In addition to Hicksonella spiralis, he described 

 Hicksoiiclla flagellata sp. nov., and Hicksonella capciisis 

 sp. nov. Mr. E. Heron-Allen read a note, prepared by himself 

 and Mr. A. Earland, " On some Varietal Forms of Massilina 

 secans." After referring to several varietal forms that had 

 been previously described, the authors related the finding of 

 numerous specimens of three of these varieties in observation 

 tanks where some gatherings of Foraminifera made oft" Selsey 

 Bill had been placed, and where they multiplied. I'he con- 

 clusion arrived at was that these variations were caused by 

 the want of sufficient shell-making material, the calcium 

 carbonate in the tanks having been used up, the sea-water 

 never ha\ing been renewed. A note by Mr. E. M. Nelson on 

 "A Micrometric Difficulty," was read. The author referred 

 to the difficulty of counting correctly the number of ruled lines 

 or diatomic striae in a given space. The trouble does not 

 arise when the interspaces are relatively wide compared with 

 the breadth of the lines, but it does so when the breadth of 

 the interspaces approaches that of the lines. It is the black 

 and white dot image that is responsible for the trouble. When 

 the focus is at a white-dot image, the white lines must be 

 counted, and vice versa when the fppns gives a black-dot 

 image. Another paper by the same iuthor was also read, 

 " On the Resolution of New Detail in a Coscinodisciis 

 astcrompJialns." This had reference to the resolution of 

 further detail obtained by a new i" objective by Zeiss, 

 described in a pre\ious communication. The new detail 



