500 THUMAS II. 13RYCE. 



may be gathered from tlie description of iin ogg continuously 

 observed in the living state. At the lieight of its develop- 

 ment the egg monaster lay at one side^ the sperm amphiaster 

 at the other^ and no spindle was formed between them. The 

 egg divided into three cells, two larger and somewhat 

 irregular containing two daughter sperm nuclei, and a small 

 one in which the single egg nucleus re-formed. At the second 

 division each of the sperm nuclei gave rise to a perfect amphi- 

 aster, and divided into two, the accompanying cytoplasmic 

 division resulting in the formation of two complete cells and 

 one biuucleate cell. The single egg nucleus gave rise to a 

 tetraster, and divided into three cells, one binucleate, the 

 nuclei of the latter quickly fusing together. The embryo 

 now consisted of six cells — three containing maternal, three 

 paternal nuclei. At the ensuing division fifteen cells were 

 foruied, of which eight larger ones contained paternal nuclei, 

 while seven much smaller ones containing maternal nuclei lay 

 in a definite group at one side. The egg observed afterwards 

 died. Wilson has not seen an egg monaster become dicen- 

 tric at the first division, but the above observations prove 

 that it may operate as an effective division centre, without 

 establishing a spindle connection with either of the sperm 

 asters, and that it may divide later. A centrosome was 

 demonstrated in the monaster, in the same form as in the 

 sperm aster, and as in magnesium eggs. The possible action 

 of the chemical as the exciting agent of the karyokinetic 

 transformation was excluded by control experiments, and it 

 was therefore concluded, that it was due to a stimulus effected 

 by the spermatozoon, as in Ziegler's experiment. 'J'hese 

 observations, added to the results obtained in the magnesium 

 eggs, " demonstrate that under appropriate stimulus the egg 

 may give rise to a centrosome ca])able of progressive division, 

 but the etherised eggs show in the clearest manner that this 

 centrosome is less effective than the sperm centi-o- 

 some." 



I shall not venture on the general problem of the asters and 

 centrosomes. It will suffice for the present purpose if it be 



