86 



RDWICKE'S SCIENCE-GOSSIP. 



neck on the top of which i^perched the'head, consisting 

 of three beautifully reU'culated forceps-like blades or 

 jaws, armed, except in the smallest kind, Stereophylla, 

 with strong sharp serrated teeth. In Globifera the 

 head is placed directly on the stem without any inter- 

 vening neck. In their natural state these calcareous 

 head?, as well as the stems, are clothed with a sarcodic 

 covering, especially abundant and dilated in Globifera. 

 But when treated with potass this is dissolved, and 

 the skeletons only left. 



It is an interesting experiment to cut out with a pair 

 of scissors, which can be easily done, the membranous 

 portion surrounding the mouth of the Echinus, and 

 detaching it from the five prominent teeth protruding 

 through it, and familiarly known by the fanciful name 

 of Aristotle's Lantern, to place it in some sea-water on 

 a glass slip under the microscope. The animal must be 

 undoubtedly dead, but on the severed portion under 

 examination the pedicellarise will be seen still in a 

 lively condition, bending their extensile necks in every 

 direction, and opening and shutting their three- 

 bladed jaws. 



I have now only to add a few words on the possible 

 functions of these pedicellarire, though nothing is 

 known conclusively on the subject. Their first dis- 

 coverers considered them to be parasites perfectly 

 independent of their hosts ; but this cannot be the 

 case for various reasons, as in the first place they are 

 invariably present in the same numbers and in the 

 same position, which would not be the case were they 

 adventitious ; and secondly their skeletons are formed 

 of precisely the same material and on exactly the same 

 structural plan as that of the creature's test on which 

 they rest ; whilst the sarcodic envelope surrounding 

 them is a mere continuation of that which clothes the 

 entire shell as well as the spines upon it. Perhaps 

 the best suggestion as to their use is, that they catch 

 and hold in their grasp the small crustaceans swim- 

 ming past, and that these, dying and decaying, attract 

 around them clouds of minute infusoria, which event- 

 ually become the prey of the Echinus ; but this is a 

 mere theory which must be taken for what it is 

 worth. 



MICROSCOPY. 



Cement for Glycerine.— Every one who has 

 had much experience in microscopy recognises the 

 extreme value of glycerine as a mounting medium, 

 but the evil reputation it enjoys for "leaking" has 

 much restricted its use. The cements in common 

 use are not to be relied upon. Dammar varnish, so 

 strongly recommended by some, becomes so saturated 

 and softened that after a few months, cover, specimen 

 and cement may often be wiped off the slide with the 

 greatest ease. Even good gold size is not safe, and I 

 believe chiefly for the reason that many bad specimens 

 of this varnish are in the market. Having experienced 



much inconvenience from the want of a reliable 

 cement, I am glad to believe that I have at length 

 succeeded in obtaining one. The description is to be 

 found in Dr. Marsh's book on " Section Cutting" (a 

 notice of which you gave recently), and as the in- 

 formation will doubtless be welcome to many besides 

 myself, I send you the following extract, which 

 perhaps you may consider worthy of preservation in 

 your pages. ' ' The great drawback to the use of 

 glycerine is the extreme difficulty experienced in 

 preventing its escape from beneath the covering- 

 glass, for it unfortunately possesses such great pene- 

 trating power that no cement hitherto devised can 

 be thoroughly depended upon for withstanding its 

 solvent action for any considerable length of time. 

 Attention to the instructions however presently 

 to be given will however reduce this risk of leak- 

 age to a minimum : after clearing away all super- 

 fluous glycerine from round the cover, with a 

 very small camel's-hair pencil, charged with solu- 

 tion of gelatine, a ring must be made round the 

 margin of the cover of sufficient breadth to take in 

 both cover and slide. As this cement is perfectly 

 miscible with glycerine, it readily unites with any of 

 that fluid which may ooze from beneath the cover 

 and which in the case of any of the ordinary varnishes 

 would act as a fatal obstacle to perfect adhesion. To 

 make the cement, take 5 oz. of Nelson's opaque 

 gelatine, put it in a small beaker, add sufficient cold 

 water to cover it, and allow, the mixture to remain 

 until the gelatine has become thoroughly soaked. 

 The water is now pouted off and heat applied until 

 the gelatine becomes fluid, when three drops of 

 creosote should be well stirred in and the fluid 

 mixture transferred to a small bottle to solidify. 

 Before use this compound must be rendered liquid by 

 immersing the bottle containing it in a cup of warm 

 water. When the ring of gelatine has become quite 

 set and dry (which will not take long) every trace of 

 glycerine must be carefully removed from the cover 

 and its neighbourhood by gently swabbing these parts 

 with a large camel's-hair pencil dipped in methylated 

 spirit. After drying the slide, a ring of Bell's micro- 

 scopical cement may be applied over the gelatine, and 

 when this is dry another coat is to be laid on. If 

 it be desired to give to the slide a neat and tasteful 

 appearance it is a very easy matter by means of the 

 turntable to lay on a final ring of Brunswick black or 

 white zinc cement." — William Briars, Hackney. 



Microscope Improvements. — In an important 

 paper recently read before the Chichester National 

 History and Microscopical Society, on "Microscopes," 

 Mr. F. J. Freeland reviewed the most noteworthy 

 improvements which have been made in objectives, 

 both at home and abroad, within the last five years. 

 Among other subjects, he said that "a new eighth 

 and a twelfth, designed by Professor Abbe, for use 

 with oil of cedar, and, to obviate screw collar adjust- 



