200 



HA RD WICKE'S S CIE JVC E- GO SS/P. 



HINTS FOR YOUNG MICROSCOPISTS. 

 No. 2. 



IN my last paper I referred to a steady head as a 

 requisite to correct drawing with the camera. I 

 would now direct attention to the necessity of a 

 steady hand in dissection under the compound micro- 

 scope. For ordinary purposes, no doubt, a single 

 convex lens is quite sufficient. But when delicate 

 dissections are required, one has only to transfer the 

 object supposed to be distinctly seen to the stage of 

 the compound microscope to perceive at once that 

 much had not been noticed. Supposing then that a 

 small compound microscope with B eye-piece, one 

 inch objective and an erector be used, the following 

 arrangement for a dissecting table will be found most 

 helpful. 



— ' 1 



Fig. 151. — Details of Dissecting Table. 



A strong low table of the dimensions now given, 

 and standing on four substantial legs, should be ob- 

 tained. Height twenty-two inches, top nineteen 

 inches by fifteen, the narrower width being from 

 right to left. Upon this table are placed two arm 

 supports, a side view of which is here given. Length 

 from a to I) twelve inches j width four inches, and 

 height five inches. These are so placed as to admit 

 the microscope to stand between them, and the 

 height of the arm rests should correspond with the 

 height of the stage when the microscope is placed 

 perpendicularly. The portion of the rest from o to b 

 comes over the edge of the table upon the thighs, so 

 as to afford a complete support for half the forearm. 

 These rests are attached to the table only at s, where 

 a screw passes from under the table upwards into the 

 middle of the piece of wood a s, and so enables the 

 rest to be moved as on a pivot, inwards or outwards, 

 as desired. The top of the table will be then repre- 

 sented by the figure B, where M is the microscope 

 RR the rests, L the lamp. The dissector then places 

 himself on an ordinary chair, draws himself to the 

 table so that his thighs pass under the rests, and goes 

 to work. The height of the table and of the rests 

 can easily be varied a little to suit the operator. 



The writer has tried various forms of dissecting 

 tables and rests, but has found none so completely 

 steady as the above. 



Codicote Vicarage. T. R. I. 



A NEW ROTIFER. 



I SEND you a sketch of a rotifer new to me, which 

 I have found on some weeds in one of my glass 

 aquariums. It has only one wheel or ciliated disk ; it is 

 very small, and when first observed I took it for a 

 young Tubicolaria JVajas, as like them it has an 

 irregular case of a gelatinous substance and was 

 surrounded with brownish filaments which are con- 

 tinually added to the case, and in time renders it so 

 thick that the motion of the creature within the case 

 is very imperfectly seen. I concluded that it was not 

 a young najas, as there were two eggs at the bottom 

 of the case, which had passed out of the body and 

 lodged there ; this proved to me that the creature was 



Fig. 152. — A new Rotifer. (?) 



a matured one. The eggs I carefully watched, hoping 

 to see the development of them, but the case 

 becoming so thick prevented this. I have found several 

 of them. I make them out to be about ^ inch in 

 length when fully exserted. Some of them display 

 two eyes (at a) of a very brilliant red colour. 



The jaws (at b) are large in proportion to its size, 

 and the cilia are also long, and produce by their action 

 a powerful current or vortex in the water. I have 

 observed some young ones swimming at a swift rate 

 through the water previously to their becoming fixed. 

 When first fixed down they are very transparent, and 

 the action of the circlet of cilia at the head is plainly 

 seen, and also the jaws in motion ; indeed, at this 

 time, scarcely any other parts of the body are visible 



