358* 



APPENDIX 



8. P. 53. Origin of the mitotic figure. It is not made sufficiently clear, in this brief 

 account, that the origin of the achromatic figure varies in different cases, though this fact is 

 pointed out in a number of other places (cf. pp. 49, 50). In all cases where the centro- 

 some is extra-nuclear, the asters appear to be of cytoplasmic origin and arise through a 

 radial grouping of the cytoplasmic network. The spindle, on the other hand, may be en- 

 tirely of intra-nuclear origin, being formed from the linin-network (in many plant cells and 

 embryonic animal cells) ; or it may have a double origin, the central spindle being formed 

 outside the nucleus, while the mantle-fibres arise, in part at least, from the linin-network 

 (spermatogonia of the salamander, Fig. 21, etc.). The difference presents no difficulty in 

 view of the fact that the linin-network is no more than the intra-nuclear part of the general 

 cell-reticulum (p. 214), from which the entire amphiaster is formed. 



9. P. 82, 1. 23. The -connection between the attraction-spheres has been shown by 

 Meves (A. m. A., XLVIII. I, '96) to be the remains of the central spindle. 



10. P. 112, Foot-note 2. In Hydra many of the ovarian cells break up and their nuclei 

 are ingulfed by the ovum to form the "pseudo-cells." (Brauer, Z. 20. Z., LII., '91.) In 

 Tubularia a number of germ-cells fuse to form a syncytium, in which the nucleus enlarges 

 to form the germinal vesicle, while the others degenerate as pseudo-cells. ( Doflein, Z. w. Z.> 

 LXII. i, '96.) 



11. P. 125, 1. 38. Meves (Mittk. f. d. Ver. Scklesia.- Hoist., Aerzte, V. 5, '97) has estab- 

 lished the truth of Hermann's conjecture by tracing the " Nebenkorper " to the attraction- 

 sphere of the early spermatid. At an early period it contains two centrosomes which are 

 said to give rise respectively to the ring and to the deeply staining sphere. The latter en- 

 larges to form the middle-piece; the ring does not form the "fin," as Hermann believed, 

 but the posterior end of the middle-piece, and is homologized by Meves with the " end- 

 knob " of Ballowitz. The axial filament grows out from the more peripherally placed cen- 

 trosome which afterwards gives rise to the ring, and it has no connection with the nucleus. 



12. P. 156, last line. Through a misapprehension of Van Beneden's meaning, I have 

 incorrectly stated his opinion regarding the origin of the centrosomes (see Science, V. 105, 

 Jan. i, '97). He did not in fact commit himself to any positive conclusion, but somewhat 

 doubtfully expressed the opinion that both attraction-spheres, and hence by implication 

 both centrosomes, were probably derived from the egg, i.e. from the second "pseudo- 

 karyokinetic " (maturation) figure. 



13. P. 159! Lillie (Sfience,V. 114, March 5, '97) has reached the remarkable result 

 that in the lamellibranch Unio both egg- and sperm-centrosomes disappear, the cleavage- 

 centrosomes being a new formation of maternal origin. 



14. P. 159, Foot-note. For Hertwig's full paper, which is of great interest and impor- 

 tance, see Festschrift fur Gegenbaur, Engelmann, Leipzig, '96. 



15. P. 192, 1. 3. Meves's new and very thorough investigations (//. m. A., XLVIII. 

 i, '96) lend no support to vom Rath's account. There are but two generations of sperma- 

 tocytes and two " maturation-divisions." The first of these is of the heterotypical form, but 

 no tetrads are formed, and the second division occurs by longitudinal splitting of the chro- 

 mosomes. Both divisions are interpreted as "equation-divisions," and there is therefore no 

 reduction in Weismann's sense. All these conclusions are sustained by observations on 

 Amphiuma made by Mr. J. H. McGregor, in the Columbia laboratory. Reduction in the 

 amphibia would therefore seem to take place substantially in the same manner as in 

 Ascaris. 



16. P. 192, summary. The origin and meaning of the tetrads still remains problem- 

 atical, and some of the recent work shows the necessity for great caution in the attempt to 

 draw general conclusions. In a recent paper (A. m. A., XLVIII. 4, '97) von Klinckowstrom 

 describes and figures tetrads in the second polar spindle of Prosthecerceus, a Platode. R. I lert- 

 wig {Festschrift f. Gegenbaur, Leipzig, '96) has observed them as an abnormality in the 

 <r/<?0z//2g<?-spindle of unfertilized sea-urchin eggs after poisoning with strychnine. The first 



