KARYOKINESIS AND 1TS RELATION TO FERTILIZATION. 221 
in all its details, and was not rightly interpreted by a single 
observer. I do not hesitate to regard the statements of these 
authors as the most important with which our science has been 
enriched. This is evidenced in the vast impulse which they have 
given to numerous works, partly speculative, partly directed to 
the discovery of new facts and to the confirmation or refuta- 
tion of earlier statements. One must admit that the observers, 
Biitschli, Auerbach, O. Hertwig, and E. van Beneden, have not 
permitted themselves to travel further in their speculations 
than their very careful and numerous researches allowed. 
The gaps in direct observation, above noted, were in part 
filled up later by O. and R. Hertwig (96) and by E. van 
Beneden (28, 24) themselves, as well as by R. Hertwig (94, 
95), H. Fol (66, 67), Greeff (80a), Selenka (186), Mark (131), 
Calberla (45), Kupffer (117—120), Flemming (57—61), Hensen 
(88—90), Giard (78), Weismann (203, 204), Nussbaum (146— 
148), Carnoy (47, 48), Zacharias (210), Boveri (84—36), and 
others; but, as is usually the case in the progress of physical 
science, new researches and new facts provide new problems, 
and the field now in question opens up to us so wide an horizon 
that Virchow’s words (‘Gesammelte Abhandlungen,’ p. 737) 
gain more and more value. ‘“ Die Entstehung und Entwicke- 
lung der Eizell im mitterliche Korper, die Uebertragung kér- 
perlich und geistiger Eigenthimlichkeiten des Vaters durch 
den Samen auf dieselbe beriihren alle Fragen welche den 
Menschengeist je tiber des Menschen Sein aufgeworfen hat.” 
It is impossible to record here the results of all these several 
works ; it can only be mentioned that the first definite state- 
ment as to the continuity of Hertwig’s ‘‘ Spermakern ” with the 
head of the penetrating spermatozoon, as well as the observa- 
tion of the entrance of the latter, is due to Fol.! 
1 Although I here name Fol as the one who first recognised, without 
doubt, the morphological continuity in the Echinoderms between the nuewly- 
penetrated spermatozoon and Hertwig’s Spermakern, yet I am quite aware 
that earlier statements as to the entrance of the spermatozoon into the egg, 
or at least through the egg-membrane, were made by many observers: e. g. 
Bischoff (‘ Bestatigung, &c.,’ Giessen, 1854), Meissner (‘ Zeit. fiir wiss. 
Zool.,’ vi), Weil (‘ Med. Jahrb.,’ published by S. Stricker, 1873), Hensen (‘ Zeit. 
