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PROCEEDINGS OP SOCIETIES. 
to give a definite opinion upon it would require a great deal of attention. 
He could not help thinking that there was a great deal more yet to be 
done with respect to object-glasses. 
Mr. Slack said he should like to ask Mr. Brooke what would be 
the effect of rays entering the object-glass which had not passed through 
the focal point. Could they be reliable ? 
Mr. Brooke thought that the only effect they could produce would 
be a sort of confusion of light commonly known as “ milkiness ” in the 
field. 
Mr. H. J. Slack said that a few days ago he happened to be looking 
at some objects in the water from a spring, and found amongst them a 
species of diglena — he believed it to be lacustris. Diglena was a very 
difficult genus to draw, because its parts were extremely mobile. It 
was capable of protruding its jaws and moving the margin of the mouth 
aperture to such a degree as to entirely alter its appearance. In the 
instance to which he drew attention the diglena was swimming about, 
and in the course of its movements it happened to get a flip from the tail 
of another creature, an anguillula. It immediately turned sharp round, 
like an angry dog, went after the anguillula and seized it near the 
middle, and gave it a number of bites, worrying it much in the same 
way as a terrier would a larger animal that it was unable to overcome. 
Once it got hold of the tail and partially swallowed it, but not being 
able to make much of that, it let go, and the fight went on for about 
ten minutes, at the end of which time the anguillula was bitten nearly 
through, and the diglena then went its way. There did not seem to 
be any desire to eat the anguillula, but merely to worry and punish it. 
Mr. Gosse pointed out that rotifers of the genus diglena were amongst 
those which could protrude their jaws, and he said in his paper in the 
‘ Philosophical Transactions ’ : “In diglena and its allies the man- 
ducatory apparatus approaches most nearly to that of a predaceous 
insect.” He thought it worth mentioning because he had not noticed 
such conduct before, and he did not remember anything having been 
noted on the subject of angry rotifers. 
The thanks of the meeting having been voted to Mr. Slack for his 
communication, 
The President announced that the next ordinary meeting of the 
Society would he held on November 7, when a paper will be read 
by the Bev. W. H. Dallinger, and one by Mr. Thomas Palmer, “ An 
Introduction to the Study of Evergreens by the Micro-spectroscope.” 
Scientific Evening, October 31, 1877. 
This meeting was well attended by the Fellows, and, as will be 
seen from the subjoined list, the objects and apparatus exhibited were 
of great interest. The thanks of the Society are due to Mr. Baker 
and Messrs. How and Co. for the loan of excellent lamps. Tea and 
coffee were served in the course of the evening, and there was much 
friendly conversation on the objects displayed. 
