PROGRESS OF MICROSCOPICAL SCIENCE. 231 



popular paper on tlie subject of Bristle-tails and Spring-tails. Mr. 

 L. S. Packard, jun., the author, describes among other structures one 

 which appears novel. He is disposed to consider it an ovipositor. 

 In the genus Achorutes, it may be found in the segment just behind 

 the spring-bearing segment, and situated on the median line of the 

 body. It consists of two squarish valves, from between which project 

 a pair of minute tubercles, or blades, with four roimded teeth on the 

 under side. This pair of infinitesimal saws remind one of the blades 

 of the saw-fly, and he is at a loss what their use can be unless to cut 

 and pierce so as to scoop out a place in which to deposit an egg. It 

 is homologous in situation with the middle j)air of blades which com- 

 pose the ovipositor of higher insects, and if it should prove to be used 

 by the creature in laying its eggs, we should then have with the 

 spring an additional point of resemblance to the Neuroptera and 

 higher insects, and instead of this sj)ring being an important differen- 

 tial character, separating the Thysanura from other insects, it binds 

 them still closer, though still differing greatly in representing only a 

 part of the ovipositor of the higher insects. 



PJioio-micrographs for the Stereoscope. — Dr. E. H. Ward has been 

 reading an important paper on this subject before the Troy (N. Y.) 

 Scientific Association. Certainly stereoscopic views of microscopic 

 objects ought to be very popular, and would, if properly taken, prove 

 most valuable to the student. Hence we think Mr. Ward's instruc- 

 tions worthy of note. He states that in order to photograph, without 

 delay, any field of view which a working microscopist deems worthy of 

 preservation, he should have a camera mounted on a plank wiiich is 

 blocked at one end for the feet of the stand used as a " working instru- 

 ment." Then, whenever desired, the eye-piece is removed, the instru- 

 ment levelled into a horizontal position and placed accurately on the 

 plank, and the magnified image instantly thrown upon the focussing 

 plate of the camera. Finding the usual band, passing around pulleys 

 and over the fine-adjustment wheel, to be a slight annoyance in carrying 

 out this plan with the stand he ordinarily uses (a large stand of the 

 " Jackson " model), he makes the fine-adjustment by a somewhat soft 

 cylinder of india-rubber lying upon the wheel. This cylinder is 

 rather more than three inches long, is an inch and a half in diameter, 

 and weighs about four ounces. It is open thi'ough its centre, like 

 a tube with thick walls and small bore, and is mounted upon one 

 end of a straight, light, wooden rod, the other end of which is sup- 

 ported on or near the top of the camera. It is pi'e vented from rolling 

 off from the fine-adjustment wheel by a horizontal wire, transverse to the 

 axis of the. apparatus, attached by a hinge-joint to a post at the side of 

 the plank, and to a pin in the end of the wooden rod which just passes 

 through, the cylinder ; and being retained not over the centre, but 

 somewhat to one side of the wheel, loss of motion is simply impossible, 

 and an extremely fine and manageable motion is secured. The un- 

 equalled facility and certainty with which this apparatus can be 

 instantly laid upon the fine-adjustment wheel, or turned back from it, 

 is sufficiently evident. 



VOL. V. S 



