Boijal Mieroscopical Society. 207 



of the former, I have employed a system of Linear Projection, on 

 which I now beg to offer the following explanatory suggestions, 

 not however to those my seniors in the service, but more particularly 

 to younger workers as hints for their guidance, who, while pos- 

 sessing instruments furnished with good powers, and such accessory 

 apparatus as the camera lucida or other reflecting media, invaluable 

 in the case of mounted objects, will nevertheless meet with instances 

 in which such useful accessories fail to afford the assistance required 

 for the correct dehneation of certain objects ; and I trust that these 

 suggestions as to the process I employ may, under such circum- 

 stances, be found accej)table. 



In the special instances of tube-dwelhng rotifers the difficulty 

 with a camera is insurmountable, inasmuch as the restraint neces- 

 sarily imposed upon animals under observation at once obstructs 

 that freedom of action which is necessary for their assumption of 

 the expanded state, in which, with their constantly varying atti- 

 tudes, the employment of any reflector would be wholly inefiicient ; 

 and with the indifferent aptitude which I possess, regarded from an 

 artist's point of view, I have had recourse to this system as being 

 the most expedient to employ. I first make hand-sketches of the 

 object under observation, and, with the micrometer inserted, measure 

 up the work, and then set it out to scale, so to speak, and in so 

 speaking I must beg permission to use these sliop terms somewhat 

 fi'eely in the following remarks as the most expressive that suggest 

 themselves to a mechanic impressed with an intuitive predilection 

 for the tvheel animalcules in treating a subject which is not scien- 

 tific. Should, however, these and other technical expressions, such 

 as may hereafter be applied, meet the objection of scientific savants 

 as being mal a pro])os and indefinite, I can only excuse them on 

 the ground of their being most convenient terms, as here employed, 

 to distinguish the different views of an object, and I only trust that 

 with the working members their adoption may be accepted, the 

 process understood, and that their employment will not interjDose in 

 elevating the results to a position somewhat higher than that of the 

 mere mechanical. 



But, before proceeding to describe the process, I must beg per- 

 mission to specify some of the necessary tools and appliances which 

 — in addition to a good set of drawing instruments — will be found 

 necessary for the due performance of the work ; and these should 

 consist of a carefully-made drawing-board, a T square provided with 

 an adjusting stock, for the purpose of producing a repetition of 

 parallel lines at any other than a right angle, a couple of vulcanite 

 set-squares, one at an angle of 45° and another at 60^, which also 

 affords its complement of 30°, to which may be added a few para- 

 bolic curves; but as to these last it will generally be found more 

 expedient to set out on cardboard, and to cut therefrom, such par- 



