MATURATION AND FECUNDATION OF THE OVUM. 131 
into the “ Amphiaster de rebut/’ or “ directive spindle.” The 
formation of the directive spindle from the germinal vesicle is 
not fully described in the works previous to Van Beneden’s. 
On this point Yan Beneden is very clear and decided, and so 
far his account agrees with the descriptions of karyokinesis. 
But in his description of the structure of the figure produced 
and the formation of a polar globule from it, he is directly at 
variance with previous writers, and the process he describes is 
quite different from karyokinetic division. Fol and Hertwig 
describe and figure these later stages as identical, except in 
very minor points such as the length of the chromatic ele- 
ments, with the division of cell nuclei, and they give the same 
account for very different animals ; e. g. Echinoderms, Mol- 
luscs, Leeches. It follows, then, either that O. Hertwig and 
others were mistaken, or that Yan Beneden is wrong, or that 
the processes in Ascaris megalocephala are fundamentally 
different from those in other animals. Van Beneden himself 
mentions two very recent publications which support the 
theory of the cellular nature of polar globules. One is by 
Trinchese, 1 the other by Blochmann, 2 and they have shown 
that the division of the first polar globule after its expulsion 
which had been observed by O. Hertwig, again exhibits the 
phases of karyokinesis. It will naturally be expected that 
ultimately the process of formation of polar globules will be 
proved to be essentially the same in all animals, but future 
researches must decide on this point. As is well known, a 
directive spindle has been sought in vain in the ova of Verte- 
brates, and the expelled elements in these are not globular in 
form. Hoffmann 3 alone has described an Amphiaster de rebut 
in Teleostean ova, but has not traced its history. 
Several papers have appeared subsequently to Yan Beneden’s 
memoir, on the subject of fecundation, &c. P. Hallez, 4 in 
March, 1884, published a note of researches on Ascaris 
1 ‘Mem. Acad. Lincei,’ tom. 7. 
2 ‘ Z. f. w. Z.,’ Bd. xxxvi. 
3 ‘ Natuurk. Verh. Koninkl. Acad. Deel./ xxi. 
4 ‘ Comptes rendus/ No. 11, tom. 96, 1881. 
