154 



SCIENCE- GOSSIP. 



radular cartilage, upon the floor of the mouth, 

 while the longer hinder portion is lodged and 

 formed within a large radular sac. which in reality 

 is a deep cylindrical depression of the floor of the 

 mouth. When the radula is very long, as in the 

 limpet, the radular sac lies free, folded several 

 times upon itself, within the body cavity imme- 

 diately between the viscera and the muscular foot 

 disc. Throughout life new teeth are continuously 

 added by secreting cells situated at the blind end 

 of the radular sac ; the singly-refractile core of 

 each tooth being secreted by certain cells upon 

 the floor of the sac. while the enamel-like, doublv- 

 refractile outer layer is laid on by those of the 

 dorsal wall. As above mentioned, that part of the 

 radula which is in use plays over a pulley-like 

 cartilaginous cushion, and by the alternate con- 

 traction of two sets of muscles, protractors and 

 retractors, attached at one end to the base of the 

 cushion and at the other to the radula, the latter 

 is dragged backwards and forwards over the 

 cartilaginous pad, as an ostler polishes the inside 

 of fixed rings by pulling a cloth to and fro within. 

 Listen to the limpets as they rasp slowly over 

 the rocks, and you will understand clearly how 

 effective is this radula in scraping off minute 

 vegetation that coats the rock. The sound given 

 out is too definite to be mistaken. The scraping 

 action of the radula is also easily studied in a 

 fresh-water aquarium containing a few water- 

 snails. As the teeth in front wear down, the ribbon 

 is bodily moved forward sufficiently to permit new 

 teeth to come into use." Then follows a detailed 

 description of the teeth and of the classification. 

 From the notes accompanying a miscellaneous set 

 of slides we extract the following remarks on a 

 slide showing the prismatic raphides in the cuticle 

 of onion (Allium cepa) : " Lime enters largely 

 into the composition of all organic bodies. In 

 human bones, for example, the salts of lime con- 

 stitute 65 per cent, of the whole mass, or more 

 than double the amount of animal matter. There 

 are very few plants in which these limy crystals 

 or raphides are not found. They vary considerably 

 in size and shape, and it is by no means difficult to 

 detect them by cutting thin sections of plants and 

 examining them under the microscope. A glass 

 slip, a cover-glass, and a little water are all the 

 mounting materials necessary. They will not, of 

 course, come out so clearly as in a slide made by a 

 professional mounter ; but it is always interesting 

 to do something for oneself, and facts observed in 

 this way are firmly impressed on the memory. 

 The simplest form of raphides is to be found in the 

 lilies, where these bodies occur in the form of 

 bundles of needle-like rods occupying the centre 

 of the cell. In the strip from the outside of a lily 

 stem they will be seen under an inch as an almost 

 solid mass in the protoplasm of the cell ; but the 

 J-inch will resolve this mass into its constituent 

 parts, when the needle-like bodies lying side by 

 side can be made out distinctly. ■ In the onion the 

 raphides are prismatic in form, and may be seen 

 scattered over the whole section ; the walls of the 

 cells in which they are enclosed can be clearly 

 made out. and each cell contains a single crystal 

 or raphis." 



Mounting Methods. — I shall be much obliged 

 by such information as will enable me, first, to 

 prepare and mount in balsam a portion of the 

 snare of Epeira diadema ; second, to devitalise 

 and prepare for mounting for tup-light, lepidop- 



terous and other insect eggs. For devitalising I 

 have tried momentary immersion in boiling water 

 and maceration in spirit, turpentine, and benzole ; 

 but my professional mounts are certainly not pre- 

 pared so. — F. M. BroJiensMre, Exeter. 



[Can any of our readers give any information on 

 these subjects ' We have never attempted to 

 momit the threads of a spider's web in any other 

 way than dry in a closed cell. We would not 

 consider Canada balsam a suitable mount, as its 

 refractive index so nearly approaches that of the 

 web as to render the latter almost invisible, if 

 clean. There is also the danger that it might 

 prove soluble in this medium. Mr. A. B. Lee re- 

 commends the fixing of insect ova by means of 

 heat, which may be followed either by alcohol or 

 some watery hardening agent : but his methods 

 are all directed to embryological requirements. 

 Dr. Carpenter says : " In order to preserve insect 

 eg - gs they must be mounted in fluid in a cell, since 

 they will otherwise dry up. and may lose their 

 shape." Simple immersion in hot water should 

 suffice to kill the eggs ; but there would still be 

 the danger of subsequent shrinkage if mounted 

 dry. — Ed. Microscopy, S.-G.j 



MEETINGS OF MICROSCOPICAL SOCIETIES. 



Royal Microscopical Society. — 20 Hanover 



Square, October 16th. 8 p.m. 

 Quekett Microscopical Club. — 20 Hanover 



Square, October 4th. 7 p.m. : October 18th, 8 p.m. 



Excursion, Oct. 5th, Xorbiton, for Richmond Park. 



[For further articles in this number on Micro- 

 scopic subjects, see pp. 133. 138. 140 and 148.] 



EXTRACTS FROM POSTAL MICROSCOPICAL 

 SOCIETY'S NOTEBOOKS. 



[Beyond necessary editorial revision these ex- 

 tracts are printed as written by the various 

 members. — Ed. Microscopy, S.-G.] 



Insect Anatomy. 



(Continued from pane 123.) 



EristaUsTenax, Longitudinal Section of Halter. — 

 For convenience of examination the halter of the 

 fly may be divided into three separate parts, viz. 

 base, pedicle, and globe or head. On the exterior 

 surface of the base there are three distinct ai<_-a> 

 or sets of sense organs which have severally an 

 anterior, posterior, and lateral aspect. These have 

 long been considered special sense organs. The 

 lower area is somewhat rounded on the face, and 

 covered with delicate elevations of the epidermis 

 which take the form of circular papillae. They 

 are divided into rows, and between each row there 

 is a line of curved hairs. Lowne states that there 

 are two distinct sets of these lower organs, and 

 Theobald in his work on the ■• British Flies " has 

 repeated this statement ; but in no instance have I 

 met with more than one, and it has invariably a 

 lateral aspect. The two upper organs are placed 

 on opposite sides of the halter, one anterior and 

 the other posterior. They are much longer and larger 

 than the lower one, but like it in having rows of 

 ridges beset with papillae separated by fine hairs. 

 Several sections show the lining epithelium re- 

 markably well. In this place it is especially 

 modified to form a sensory or nerve epithelium. 

 The pointed ends of the cells are seen penetrating- 



