38 



THE AMERICAN MONTHLY 



[February J 



serves a record of some of them in that 

 way. One of his latest productions is 

 from a shde contributed to one of the 

 boxes by ourselves, a hydroid zoophyte 

 with extended tentacles, Halccimn hale- 

 cimn. The cilia are plainly suggested by 

 the photograph, although certainly not 

 visible — probably not in the preparation 

 itself. Among other good photographs, 

 all taken with Beck's lenses, are the eye 

 of a drone fly and a transverse section of 

 a nerve. 



— The best stage-micrometer we have 

 seen has recently been made by Prof. W. 

 A. Rogers for the National Museum. It 

 is not better in ruling than others from 

 the same source, but its peculiar excel- 

 lence is due to the fact that it is mounted 

 in Prof. Hamilton Smith's new medium 

 of high refractive power. The result is, 

 that the fine lines are far more visible 

 and sharp than on ordinary micrometers. 

 Very fine lines, which are scarcely visible 

 otherwise, are readily seen when mounted 

 in the new medium. 



— Messrs. H. R. Spencer & Co. have 

 issued a neat price-list of objectives made 

 by them. They guarantee their objec- 

 tives to be strictly as represented, and no 

 goods will be sent on approval. This is 

 good business policy for those who are 

 sure their goods will satisfy purchasers. 

 It shows a determination to send out first- 

 class work. They offer also some cheap 

 but well-made microscope stands, vary- 

 ing in price, with objectives, from $42.00 

 to $83.00. 



— An excellent method of studying the 

 minute forms of pond-life has been seve- 

 ral times mentioned in these columns, 

 both editorially and by correspondents 

 who have adopted it. This is by sus- 

 pending glass slips in ponds until they 

 are covered with vegetation and infusoria. 

 It is called to mind once more by the in- 

 vestigations of alga; by L. Kny. He sus- 

 pends a slip of glass in a cylinder of 

 water and allows it to remain until covered 

 with the growths he desired to study. The 

 plan has much to recommend it, as the 

 organisms can be studied without disturb- 

 ing or removing them from the sub-strata 

 on which they grow. 



— The medium of high refractive index 

 discovered by Prof. Hamilton Smith, and 

 mentioned from time to time in these col- 

 umns, has engaged his attention for a long 

 time. He now believes it can be made 

 perfectly permanent. Heretofore it has 

 become cloudy after a time, and speci- 

 mens mounted in it spoiled. The com- 



position has not been made public, for 

 good reasons, although it is not a secret 

 with himself alone, being known to seve- 

 ral persons. It will be made known in 

 due time. The experiments made by 

 Prof. Smith in the course of his work to 

 find very highly refractive media have led 

 to the discovery of several preparations of 

 this character, which inay yet be used 

 with great advantage. They are easily 

 prepared, and are sure to be employed 

 when the method of making them is pub- 

 lished. 



— In Doital Cosmos, November, 1884, 

 Dr. J. L. Williams has an interesting and 

 valuable article 'On Certain Disputed 

 Points in the Development and Histology 

 of the Teeth.' It is illustrated by wood- 

 cuts and two heliotype plates. The sub- 

 ject is rather too technical to be noticed 

 at length without giving more space than 

 can be spared in these columns. Dr. 

 Williams, it will be remembered, has pre- 

 pared some fine sections of teeth by the 

 method described in vol. v, p. 142. 



— Some time ago a gentleman in Paris 

 purchased a one-inch objective of very 

 wide angle of American manufacture, and 

 as it may be of interest to know the esti- 

 mate put upon it in Paris we quote a few 

 words from a private letter recently re- 

 ceived. ' After careful examination and 

 showing it to friends, we do not find that 

 it has any advantage over a Nachet, 

 which he supplies for 25 francs, ($5.00). 

 There is more light, a point of very little 

 importance in so low a power, it has not 

 any greater defining power on test plates, 

 but its great defect is want of aplanatism 

 — the edges of objects are dreadfully dis- 

 torted.' 



— Mr. H. G. A. Wright recently de- 

 scribed a preparation of the proboscis of 

 a blow-fly mounted without pressure in a 

 solution of biniodide of mercury in iodide 

 of potassium, which was said to reveal 

 details of structure in the pseudo-trachea 

 not hitherto observed. Without entering 

 into particulars, we draw attention to the 

 fact, which suggests a more extended use 

 for this highly refractive medium. 



— Mr. A. D. Michael has described a 

 new acarus of the genus Myobia, which 

 was found on bats, particularly the Rhiiio- 

 lophus hipposidcros. The description is 

 published, with plate, in \\\(i. Joi(r. Onekctt 

 Micr. Club, Ser. 2, vol. ii, p. i. 



— A gentleman in Europe, who has 

 recently obtained a j',y homogeneous im- 

 inersion by H. R. Spencer & Co., writes 



