( 27 ) 

 SUMMARY 



OF CURRENT RESEARCHES RELATING TO 



ZOOLOOY AND BOTANY 



{principally Invertehrata and Cryptogamia), 



MICROSCOPY, &c., 



INCLUDING ORIGINAL COMMUNICATIONS FEOM FELLOWS AND OTHEES.' 



ZOOLOGY. 



A. GEIl'EIlAIi, including Embryology and Histology 

 of the Vertebrata. 



Influence of Gravity on Cell-division. t— Dr. E. PflUger's experi- 

 ments were conducted with, the eggs of the frog. Each egg consists 

 of a dark and a light hemisphere, and after fertilization the dark 

 hemisphere always comes to lie uppermost, the " axis " of the egg 

 being therefore vertical. When the black hemisphere is uppermost 

 the line connecting its middle point with the middle point of the 

 white hemisphere is termed the " primary axis" ; to the primary axis 

 correspond, of course, a primary equator and meridian. The " secon- 

 dary axis " passes through the point at which the first and second 

 planes of cleavage cut each other. The "tertiary axis" finally is 

 any perpendicular diameter of the egg that is not coincident with 

 either of the two former axes. The first two cleavages pass through 

 the axis of the egg, and the third cuts it at a right angle ; the question 

 therefore arises, is there any real connection between the direction of 

 cleavage and the axis of the egg, or do the first cleavages pass through 

 the axis of the egg because it happens to coincide with the direction 

 of gravity? By preventing the rotation of the eggs, by fixing 

 them to a watch-glass in various positions after fertilization. Dr. 

 Pfliiger was able to show that the latter interpretation is the correct 

 one ; the first cleavages do not follow the axis of the egg but the 

 direction of gravity passes along the vertical diameter, whether it 

 happens to coincide with the axis or not. In the normal egg left to 

 assume its own proper position with the dark hemisphere uppermost, 

 it is well known that the process of division is far more energetic in 

 the upper dark hemisphere, and this was believed to depend upon 



* The Society are not to be considered responsible for the views of the 

 authors of the papers referred to, nor for the manner ia which those views 

 may be expressed, the main object of this part of the Journal being to present a 

 summary of the papers as actually published, so as to provide the Fellows with 

 a guide to the additions made from time to time to the Library. Objections and 

 corrections should therefore, for the most part, be addressed to the authors. 

 (The Society are not intended to be denoted by the editorial " we.") 



t Pfliiger's Arch, f gesammt. Physiol., xxxi. (1883) pp. .311-8. 



