430 



MERISTIC VARIATION. 



[part I. 



III. Cell-Division. 



*641. It was purposed at this point to have introduced an account 

 of Meristic variations observed in the manner of division of nuclei 

 and cells ; but I have found that, to give adequate representation 

 of these facts even in outline, it would be necessary not only to 

 treat of a very complex subject with which I have no proper 

 acquaintance, but also greatly to enlarge the scope of this work. 

 But were no word said on these matters, indications most useful 

 as comment on the nature of Meristic Variation at large would 

 have to be foregone ; and unwilling that these should be wholly 

 lost I shall venture briefly to allude to so much of the matter as 

 is needful to shew some ways in which the facts of abnormal cell- 

 division can be used in reference to the wider question of Meristic 

 Variation. 



We have been dealing with cases of Radial repetition, and we 

 have seen that with Variation in the number of parts the result 

 may still be radially symmetrical. It therefore becomes of interest 

 to note that in the case of abnormal cell-division the result of 

 numerical change may in like manner be radially symmetrical. 

 Cells which should normally contain two centrosomes and which 

 should divide into two parts have been seen to contain three centro- 



II 



Fig. 130. Triasters. I. Tripolar division of nucleus in embryonic tissue of 

 Trout (after Hennegdy 1 ). II. Triaster from mammary carcinoma. Centrosomes 

 not shewn (from Fleaiming 2 ). 



somes (Fig. 130) prior to division into three parts, and the tri- 

 angle formed by the three centrosomes may be equiangular just 

 as may be the triangle of the segments of the abnormal Aurelia 

 (Fig. 128, V), or of the jaws of the normal pedicellaria of 

 Dorocidaris (Fig. 129). It is, I imagine, difficult to suppose 

 that the radial symmetry of each of these series of organs is 



1 Hennegut, Jour, de I'Anat. et Phys., 1891, p. 397, PL xix. fig. 9. 



2 Flemming, Zellsubstanz, Kern u. Zelltheilung, 1882, PL vm. fig. v. after 

 Martin, Virch. Arch., 1881, lxxxvi. PL iv. 



