18 THE AMERICAN MONTHLY [Jan 
ing on the same axis, by which a medium or an extremely 
slow movement could be obtained at will. Some new 
forms of “differential screw’’ movement were employed to 
this end. The method recommended for the Continental 
form of microscope had been arrived at independently 
and put into practice by Herr Reichert of Vienna. An- 
other form which was exhibited was employed, at the 
author’s suggestion, by Messrs. Beck. Mr. Scourfield 
read a paper on ‘‘Hydra and the Surface Film of Water,” 
and showed, by means of an ingenious model and by 
drawings on the blackboard, how minute objects, though 
slightly heavier than water, could remain in contact with 
its surface. This result was obtained by means of a 
waxy or water-repellent substance coming into contact 
with the surface film and forming a capillary depression. 
The author pointed out how many aquatic creatures, 
though undoubtedly heavier than water, could yet re- 
main at the surface without the aid of movement or air- 
bubbles. The hydra holds to the surface by its basal 
disc, and the author had been able to see a number of 
hyaline strands which were apparently secreted from the 
dise. The strands, though difficult to discern, were seen 
to extend considerably, thus making a ‘“‘capillary depress- 
ion” of comparatively large area. The author believes 
that this stringy secretion, intermixed as it is with glo- 
bular and ovoid bodies, is formed by the breaking-up of 
the ectodermal cells of the basal disc. In the ensuing 
discussion Mr. Karop described an analogous secretion 
in the Gregarines. Mr. Morland gave instances of the 
unexpected stresses the film of water will bear. Mr. 
Rousselet read a paper on ‘“‘Triarthra brachiata, n. sp.” 
This was an account of a new species of rotifer, and a 
specimen was exhibited under a microscope. In the en- 
suing discussion, in reply to a question by Mr. Scourfield, 
Mr. Rousselet said that he had not met with an instance 
of a rotifer making use of the surface film in the way 
