ZOOLOGY AND BOTA.NY, MICROSCOPY, ETC. 571 



surrounding liquid cytoplasm. A periodic reversal of the sol to the gel 

 state, and vice versa, has'lbeen demonstrated in the cell protoplasm during 

 division. The process may be described as follows : When the aster is 

 fully formed the greater part of the cell is a gel. The cytoplasm 

 reverses to a sol state, and the astral radiations fade out while the sphere 

 liquid collects at the two poles of the nucleus. The formation of radia- 

 tions about the spheres at each pole of the nucleus producing the 

 amphiaster is accompanied by a return to the gel state. A return to 

 the sol state takes place in the equator of the cell. The nuclear spindle 

 now divides, a constriction around the middle of the cell then follows, 

 and continues until the cell is cut in two. As a general rule the reversal 

 of the gel to the sol state starts in the equator of the cell and spreads to 

 the poles. On the other hand, the reversal of the sol to the gel state 

 commences about the sphere and spreads towards the periphery. 



The gel state in living protoplasm is not inert. Even to the eye 

 there is a constant but very gradual change among the granules 

 embedded in the cytoplasmic gel. There are appreciable differences in 

 the liquid state of the cytoplasm in certain regions and at various times ; 

 for instance, the interior cytoplasm of the unfertilized and fertilized 

 Qgg before the aster is formed is slightly viscous, whereas the contents 

 of the sphere and of the rays, and also of the hyaline area in the vicinity 

 of the forming polar body, are very fluid. The aster in its early stage 

 can be made to disappear by churning its contents with a needle. This 

 causes a reversal of the ^IlI to the i^\ state. From a study of cell- 

 division in the eggs o^ Echinarachnins, Gerebratulus, Arhacia and 

 Asterias, the investigator concludes that one of the factors concerned 

 lies in a peculiar colloidal property of protoplasm, namely, a periodic 

 reversibility in its sol and gel states. 



Photomechanical Changes in Retina of Normal and Transplanted 

 Eyes of Amblystoma Larvae.*— Henry Laurens and J. W. Williams 

 have studied the effects of light and darkness on transplanted eyes with 

 reference to the question whether the photomechanical changes can take 

 place independently of the central nervous system. The authors' method 

 is free from certain objections that might be raised against arguing 

 from cases where the optic nerve has been cut, which involves shock 

 and degeneration. The transplanted eye has never been under nervous 

 control. The results of the experiment show that pigment migration 

 and cone contraction take place in the transplanted eyes as well as in 

 normal eyes, and to a greater extent. 



Melanophores of Amblystoma Larvae. f — Henry Laurens finds that 

 the melanophores of tlie larvte of A.tigrimim\)Q\m.YQ like those observed 

 in A. punctatum and A. opacum ; they expand in light and contract in 

 darkness in both seeing and eyeless larvae. The melanophores of seeing 

 larvse that have been kept for some time (four days or more) in bright 

 diffuse light over an indifferent bottom are, however, partly contracted 



* Journ. Exper. Zool., xxiii. (1917) pp. 71-82 (1 pi. and 3 figs.), 

 t Journ. Exper. Zool., xxiii. (1917) pp. 195-205 (6 figs.). 



2q 2 



