322 SCIENCE PROGRESS. 



The succeeding events differ somewhat in different cells, 

 as the spindle fibres sometimes, but not always, become 

 equatorially centred to an intermediate body, in the division 

 plane of the daughter elements. 



Whatever be the exact course pursued, the greater part 

 of the spindle fibres eventually fuse or coalesce to form an 

 archoplasm in each new cell. Into these new archoplasms 

 the centrosomes gradually find their way, and finally come 

 to rest at the centre of each new mass. 



Thus, during the course of such divisions, the archo- 

 plasm appears to be first modified into an initial spindle 

 figure, and then into a complete one, the residual fibres of 

 which coalesce to form two new archoplasms — one in each 

 daughter cell. In this way the whole sphere has the ap- 

 pearance of persisting through successive cellular genera- 

 tions, archoplasm arising from archoplasm, centrosomes 

 from centrosomes. 



If, however, we now turn from the spermatocytes of 

 Salamandra to those of the mammalia, as exhibited in a rat 

 (Fig. II.), the persistence of the archoplasmic constituent in 

 the former, turns out to be no sure or universal guide to 

 its character as a cellular constituent ; because, in these 

 mammalian elements, although there is a large and obviously 

 similar nebenkern or archoplasm in the first place, the 

 centrosomes do not, even during rest, come to lie in its 

 interior, but remain quite free in the cytoplasm, generally 

 between the archoplasm and the nucleus (Fig. II. c). So 

 it follows that the sphere is here normally dismembered or 

 separated into two portions, one consisting of nothing but 

 the archoplasm, and the other of nothing but the centro- 

 somes. To these latter are. centred the protoplasmic radia- 

 tions, which, in the more ordinary type of sphere, would 

 abut on the outer surface of the archoplasm, and form the 

 exterior radial envelope of the sphere. 



In the second place, when division approaches and the 

 centrosomes separate from one another, a spindle is formed, 

 partly from the radiation which originally surrounded these 

 bodies, and probably also with the co-operation of some of 

 the nucleoplasm (Fig. II.). Its whole course of develop- 



