i893. NOTES AND COMMENTS. 325 



only a great and a common danger could have driven together such 

 variously-natured animals. Such danger would be found in advancing 

 waters, driving the animals to take refuge on isolated hills, or in other 

 circumscribed areas, there to meet their deaths by drowning. It is 

 noticed that while certain animals did not survive the rubble drift in 

 the west, they existed to historic times eastwards in Egypt — of the 

 submergence of which country there is as yet no evidence. 



When the upheaval followed, portions of the surface debris were 

 swept down, detached bones were carried away, other bones were 

 crushed and splintered by rolling fragments of rock ; and the drift 

 deposits Avere dispersed from various centres by the diverging currents 

 that resulted from the gradual elevation of the sea-bottom. 



Nuclear Division in Branchipus and Apus. 



Mr. J. E. S. Moore, in the Quarterly Journal of Microscopical 

 Science for September (vol. 35, pp. 259-283), has published some results 

 of great interest. In the male gland of Branchipus, the first stage 

 in spermatogenesis consists of the enlargement of the cells lining the 

 tube, and the arrangement of their nuclei into a spirem with the 

 chromatic elements all on one side. During this time, a large 

 number of bodies like centrosomes (pseudosomes), appears in the 

 protoplasm at the cell-basis. The spirem breaks up into ten dumb- 

 bell shaped chromosomes, and these arrange themselves in an 

 equatorial plate. But in this process the chief interest is that the 

 observer regards it in the light of Biitschli's froth theory of proto- 

 plasm. At first the whole nucleus appears to be made up ot drops 

 of a clear fluid, enclosed in films of staining material. These drops 

 gradually run into each other, as the drops of a soap foam grow larger 

 by smaller bubbles breaking into the larger. As this process goes 

 on the strands or meshes of staining material become thicker and 

 thicker, and ultimately break up into the chromosomes. As this 

 running together of the nuclear bubbles progresses it breaks beyond 

 the nuclear limits, and bursts into the cytoplasm. The chromosomes 

 thus are left hanging in a clear plasm, supported by a few strands 

 of the cytoplasm which have not yet been broken through. These 

 irregular strands become reduced to fine threads, and the threads 

 terminate in the pseudosomes. As a result of the tractions of the 

 films of the ' bursting bubbles, the threads with the chromosomes 

 become pulled into a spindle of which the poles are those 

 pseudosomes which have " the best foothold," on the cell periphery. 

 The other pseudosomes and their threads converge on these, and the 

 result is a more or less regular spindle. The actual centrosomes are 

 a fusion of some of these pseudosomes, and are thus in origin 

 equivalent to the angular spaces in the network exterior to the 

 nucleus. A progressive fusion of the bubbles in the cytoplasm 

 sweeps together the scanty stainable material of the cytoplasm into 



