PROCEEDINGS OF SOCIETIES. 
.267 
not reach them. He had seen it mentioned that by the introduction 
of a i-inch lens into the body of the microscope the focal length of 
the objective was increased without detriment to the power or the 
definition. He was glad to have the opportunity of asking Dr. Pigott 
if it was possible to do this, as it would be a very great advantage to 
him if he could. 
Dr. Pigott said he had often got into similar difficulties himself, 
particularly with the -^-^ inch ; but by using lenses in the body of the 
tube he had obtained the advantage mentioned, and had saved the 
covering glasses of many valuable slides. With regard to Dr. Hudson's 
question, he presumed that the power employed would be about 
200 diameters with a C eye-piece. In that case, if he would take 
another |^-inch objective to pieces, and put the back lens of it between 
the objective and the eye-piece, he would find that it would have the 
effect which he desired to obtain. 
Mr. Jas. Smith recommended the method of putting an object-glass 
below the stage and then working through it with a 3 inch above 
the stage in the ordinary manner. By this means a series of powers 
varying from 2 to 150 diameters could be obtained with a considerable 
length of fo€us, and with the advantage of the objects being seen erect. 
With a ^ inch below and a 1 inch above a different range of powers 
would be obtained ; they would in this way get not only a splendid 
range of objectives and definition, but could use it very well in tanks 
more than half an inch in depth. 
Dr. Pigott said if good definition was desired, the lower the lens 
was put down in the tube the better. 
Mr. Beck would be sorry to pass away from the very beautiful 
drawings before them to matters of detail without asking whether the 
variations from Ehrenberg's figure were more important than the fact 
that the creature did not build up a tube ? Was not this tube building 
one of the characteristics of Melicerta ? And if so, could they be 
right in classing equally as Melicerta a creature which did not build 
itself a tube ? 
Dr. Hudson said there was in all cases a gelatinous sheath, with 
foreign particles lying evenly or unevenly upon it. 
Mr. Slack said it seemed to him that if the secreting organ 
described by Dr. Hudson had a structure like that of the brick-making 
organ, the creature might be put under the same genus as Melicerta 
ringens ; but if it was not so, he thought this would be sufficient to 
make quite a generic distinction. He had suspected the existence of 
a Melicerta besides M. ringens. Ordinarily the pellets of M. ringens 
were round in shape, but by pressure together became hexagonal ; but 
he had once found a number of pellets which were quite conical in 
form, and he thought that they must have been the work of another 
species. The identification of rotifers was often rendered extremely 
difficult by their peculiar behaviour. The Cephalosiphons sent by 
him to Mr. Gosse some years ago, and figured in the 'Intellectual 
Observer,' only partially expanded their disks, and looked like some 
other species. Other specimens sent to an excellent naturalist pre- 
sented only misleading appearances. 
