i894. CELL-DIVISION. 41 



instead of two. Perhaps, however, the most curious of all these 

 pathological cases are those of ova which have been in some way 

 enfeebled, and so are unable to prevent the entrance of more than 

 one spermatozoon, a phenomenon which in these forms is abnormal. 

 Many of these spermatozoa come into contact with the Qgg nucleus. 

 There results a karyokinetic figure having three, four, or many spindles 

 and consequently double as many polar stars as there were spermatozoa 

 which reached the egg nucleus. Furthermore, those spermatozoa 

 which have entered the ovum but not come into contact with the egg 

 nucleus, may also divide karyokinetically, and combine together to 

 form figures and patterns of most varied kinds. 



The Component Parts of the Nuclear Figure. 

 It is now necessary to consider more in detail the various ele- 

 ments which go to make up the nuclear figure. From the foregoing 

 account it will be seen that the parts of a karyokinetic figure can be 



tabulated in the following way : — 



, ( Centrosomes. 



. , ,. 1 , Archoplasmic spheres. 



Achromatic elements. -I o • ji 



N-lear figure ^ I f^t 



Lame intermediaire. 

 Chromatic ,, ' Chromosomes. 



Centrosomes and Archoplasmic Spheres. — Although the so-called 

 " Polkorperchen," or " centrosome," was discovered as early as 

 1870, by Fol and others, to exist in the centre of the archo- 

 plasmic spheres during the division of the nucleus, yet even 

 at the present time opinions vary considerably as to its real 

 origin. Van Beneden, Boveri, and indeed the majority of observers, 

 look upon the centrosome as a permanent organ of the cell-body, 

 present during the resting as well as active stage, and entirely 

 external to the nucleus. Their views are to some extent borne out by 

 the fact that in several instances, e.g., epithelial cells of fishes and 

 coelomic corpuscles of Nemertines, an undoubted centrosome has 

 been found during the resting stage in close proximity to, but 

 perfectly distinct from, the nucleus. On the other hand, in few, if any 

 cases, has the centrosome been actually traced through the stages of 

 karyokinesis into the resting condition. O. Hertwig, on the other 

 hand, is opposed to this view, and maintains that the centrosome is 

 in every case essentially a nuclear structure, for the following 

 reasons : {a) it has not been demonstrated, save in a few exceptional 

 cases, as existing in the body of the cell during the resting stage ; 

 {b) its appearance is usually simultaneous with the breaking up of 

 the nuclear membrane ; [c] it has been observed to appear first at 

 the edge of the nucleus, and then gradually wander into the body of 

 the cell. 



Although the opinion of Hertwig is contrary to that of most 

 authorities, yet Brauer in Germany, and Moore in this country, have 

 recently (September, 1893) published accounts of spermatogenesis, 

 the former in Ascaris megalocephala, the latter in Branchipns, in 



