88 NATURAL SCIENCE. Feb.. 1896. 



adds that the exopodites may also be seen, though less distinctly, in 

 embryos of other isopods. Further, he finds in the development of 

 y^ra a fold which extends backward to behind the first thoracic leg 

 and represents a rudimentary carapace. Thus two of the characters 

 which separate the Chelifera from the rest of the Isopoda apply only 

 to a part of their life-history and lose at least some of their supposed 

 importance. 



In all the memoirs there are copious details worthy of discussion, 

 but there is no space left even to trace the thrilling history of the 

 *' vitellophags," or to describe that movement of the nucleus which 

 becomes at once so simple and so solemn when spoken of as 

 karyokinesis. 



The Sense of Rotation. 



In the second number of the " Princeton Contributions to Psycho- 

 logy," reprinted from the Psychological Review, under the editorship of 

 Professor Mark Baldwin, is a paper by Mr. H. C. Warren on 

 " Sensations of Rotation." Special arrangements were made to 

 introduce, in addition to the internal sensations due to rotation on a 

 turn-table, visual sensations. The subject was allowed to see, 

 through an aperture in a screen at the foot of the rotating board, a 

 number of strips of paper hung on two opposite walls of the room. 

 Behind the aperture a mirror could be introduced, thus causing an 

 apparent reversal of the direction in which the white strips seemed to 

 be moving. It is well known that when a subject is rotating at a 

 moderate and uniform velocity he supposes himself at rest. Only 

 when the velocity is altered does he have sensations of being turned 

 through a certam angle. If the uniform rotation is in any given 

 direction an increase of velocity is interpreted as a slight turn in that 

 direction, while a decrease of velocity is interpreted as a turn in the 

 opposite direction. These results were confirmed by Mr. Warren's 

 observations in a darkened room. But when the strips were illumi- 

 nated and became visible there arose a conflict between the dicta of 

 the internal sense and the dicta of the visual sense. 



From a number of experiments, of which we cannot give the 

 details, Mr. Warren draws the following conclusions : (i) that the 

 internal sense of rotation is in the head alone and is something other 

 than the general indication furnished by the vaso-motor system ; 

 (2) that the organ for the sense of rotation is the same as that for 

 progressive movement ; (3) that the results seem to favour the view 

 that the semicircular canals constitute that organ. These conclusions 

 differ from those reached on various grounds by Delage, Ayers, and 

 others ; but they seem to be drawn with caution from carefully con- 

 ducted observations. 



