312 MEMORANDA. 



scope as supposed, unless the same slide be used by all 

 observers. — A. 



On a IVe-»v liOcalitj' of I?Iicro.«iCopic Test-objects. — In a omith- 



sonian memoir published in February, 1854,* I have described 

 and figured a species of Hyalodiscus from Halifax, Nova 

 Scotia, which appeared to me to be admirably fitted for a 

 test-object, inasmuch as its circular form, with radiant and 

 curved lines of great tenuity proceeding in all directions, 

 renders it unnecessary ever to change the position of the 

 shell when in the field of view in order to secure the best 

 possible direction of the light. Whatever its position, on 

 account of the perfect symmetry of its form and markings, 

 some portion must always be in the best possible position with 

 reference to the oblique light used for its examination. Unfor- 

 tunately, the Halifax specimens of this beautiful object 

 appear to be quite rare, I am therefore happy to announce 

 the discovery upon various Algae from Monterey, California, 

 of an inexhaustible supply of a species of Hyalodiscus closely 

 allied to the Halifax species, and answering equally well as a 

 test-object, I find it so convenient as a test-object when 

 balsam-mounted that I am sure it will find favour with lovers 

 of the microscope. — Professor J. Bailey, in American 

 Journal of Science and Arts. 



menioranda on Flies' Feet. — In the Journal, Vol. iii., p. 230, 

 Mr. Tyrrell, of Newcourt, remarks, " In confirmation of 

 Mr. Hepworth and other naturalists, that the use of the 

 cushions beset with hairs terminating in glands secreting a 

 glutinous substance, is to attach the foot to the surface upon 

 which the insect walks by means of such secretion, and not 

 by suction, I would suggest that the hooks on the feet of flies 

 are intended not to attach the Fly to anything, but to be used 

 as fulcra, or props, which it can push against when it wishes 

 to detach the cushions. Without the hook-shaped props, the 

 F'ly, when once stuck Jast, must remain so." 



Mr. Tyrrell alludes to a paper in the previous Volume on 

 the ' Fly's Foot,' in which I state that this fluid is not essential 

 for that purpose (of attaching the foot), and I speak of the 

 tubules as suckers. My observations have led me to the fol- 

 lowing conclusions : viz. : that the termination of each hair or 

 tubule is a sucker, and the secretion is only to increase its 



* ' Notes on New Species and Localities of Microscopical Organisms,' 

 liy J. W. Bailey, in ' ymithsoniau Contributions to Knowledge,' Vol. vii., 

 p. 14. 



