570 SUMMARY OF CUERENT RESEARCHES RELATING TO 



by active cell-division. It does not seem probable that the differences 

 in length at different levels can be due to differences in the character of 

 the cells involved. The process must be under a more central control, 

 probably connected with general functional activity. The changes in 

 rate during the regenerative process bear a definite relation to the 

 histological processes observed. The rate of regeneration of one limb, 

 e.g. the right foreleg, is greater than when the other foreleg is removed 

 at the same time, but when a dissimilar organ, e.g. the tail, was injured 

 at the same time the rate was not altered. Incompleteness of regenera- 

 tion is of frequent occurrence. " The factors at work in bringing 

 regeneration to a close tend to overdo rather than underdo their 

 functions," 



b. Histology. 



Spleen During Hibernation.* — Frank C. Mann and Delia Drips 

 have made observations on Spennophilus tridecemlineatus during hiberna- 

 tion. Grossly and microscopically the spleen becomes intensely con- 

 gested. The maximum is reached within a few days after the animal 

 becomes torpid, and this is retained for about forty days. After 

 seventy-five days of torpidity the amount of blood in the spleen is not 

 greatly in excess of that found in the organ of active animals. There 

 are changes during hibernation in the number of phagocytic endothelial 

 cells containing red blood corpuscles or blood pigment. The intense 

 congestion of the hibernating spleen is probably due to a loss of tone 

 and relaxation of the intrinsic muscles of both the spleen and the blood 

 vessels. Perhaps the spleen acts as a store for red blood cells in the 

 early stages of hibernation, and allows them to ])e added to the 

 circulation as needed. 



The Cell Aster.f — It. Chambers publishes the second of his micro- 

 dissection studies — the cell-aster, a reversible gelation phenomenon. 

 Marine eggs, the development of which could be easily followed, were 

 used, and most of the conclusions relate to Echinarachnius and 

 Gerehratulns. He finds that the sphere is a liquid region free of 

 granules, occupying the centre of the aster, and increasing steadily in 

 size until the aster reaches full development. The increase in size is 

 apparently due to the accumulation of liquid flowing into the sphere 

 from all parts of the • cytoplasm. The aster rays appear to be the 

 channels in which the centripetal flow occurs. The cytoplasm between 

 the rays is in the gel state, to which the rigidity of the aster is due. 

 The gel state is most pronounced near the sphere, and, peripherally, 

 passes gradually in the sol state of the cytoplasm lying beyond the 

 confines of the aster. When the aster reaches the periphery of tlie cell 

 the entire cell is rendered comparatively rigid. In the maturation 

 figures of the egg-nucleus the peripheral aster forms a continuous gel 

 with the surface layer of the egg to which the figure is thus firmly 

 attached. The confines of the central aster pass insensibly into the 



* Journ. Exper. Zool., xxiii. (1917) pp. 277-84 (4 figs.). 

 t Journ. Exper. Zool., xxiii. (1917) pp. 483-506 (1 pl.).i 



