40 PBOGRESS OF MICROSCOPICAL SCIENCE, 



Calopteryx. Finally, Brandt's figure 19 may be compared with his 

 figures 8, 8a, and 9, tlie yolk now being confined to a small area on 

 the back of the embryo, wbicb is now segmented and nearly ready to 

 batcb, the claws being indicated, the eyes formed, the appendages 

 partly jointed, and otherwise much as in the larva. 



A New Metlwd of producing Stereoscopic Effect. — In a recent number 

 of ' Zehender's Monatsblat ' there is an accoimt of this new experiment 

 of Listing, who has already done so much in physiological optics. 

 It brings out stereoscopic effect with only one picture, which consists 

 of figures arranged in a peculiar way, and seen with vertical double 

 images. The simplest experiment is to view two lines crossing each 

 other at an angle of about 30°, with a prism of 4° or 

 5^^, its base vertical before one eye. No effort must be 

 made to correct the vertical dij)lopia. If the prism be 

 j)ut before the left eye, its base upward, the line B B' 

 seems nearer to the eye than A A'. If the prism be turned 

 with its base downward, and before the same eye, the line 

 A A' seems nearer, and B B' more remote. It is found 

 that with the base downward the prism must be weaker 

 than when turned with the base upward. In gaining 

 the effect by prisms so weak as these, no double vision 

 is produced except for horizontal lines — the oblique lines 

 appear to be only two. The same phenomenon may be produced in a 

 common stereoscope by having two similar figures, and pushing one 

 alternately up and down. Two rows of the same letters are arranged on 

 a page like the limbs of the letter X, and viewed as above stated with 

 a vertically deflecting prism ; a sudden removal of one now takes place 

 to a considerable depth, while this appearance is at once reversed on 

 turning the jirism around 180°. These curious effects can be best 

 produced and understood by means of the diagrams accompanying the 

 article. 



Tlie Red Blood-globule. — Dr. Eichardson, of America, who has 

 lately been inquiring into this subject, publishes some observations in 

 the American ' Medical Times.' He desires to allude briefly to one of 

 the minor points among his observations, which doubtless has been 

 overlooked, — viz. that recorded to the effect that blood crystals of the 

 Menobranchus, when jmrtly dissolved, could be seen to move raj)idly, 

 and as if with perfect freedom, in various dii-ections, between the 

 nuclei and external borders of certain corpuscles. This fact appears 

 to his mind much more consistent with the hypothesis of a cell wall 

 enclosing fluid contents than with the doctrine of a homogeneous 

 jelly-like constitution (Beale), or the theory of a crystalloid element 

 "contained in an albuminous framework of paraglobulin " ^rm enough, 

 to p-eserve the shape of the red disk (Briicke, Strieker) ; and it seems 

 to him the indication fui-nished by this circumstance resembles in 

 kind the evidence which sudden dartings of a gold-fish across his vase 

 would be that he was not imbedded in jelly or entangled within a net. 

 Fully recognizing, however, the wisdom of caution against considering 

 any one series of experiments (or, he may add, indeed, any one man's 



