No..376.]): REVIEWS OF RECENT LITERATURE. 281 
observations extend over a very wide range of forms, the applica- 
bility of the view to the whole animal kingdom has been generally 
vecepted. ° 
There has been one discordant account, however, since Wheeler, 
in 1895, published a preliminary paper’ in which he maintained that 
in the case of Myzostoma glabrum the egg centrosome persists and 
divides to form the cleavage centrosomes. This observation, coming 
from such an able investigator and being supported by the unquali- 
fied statement that no trace of centrosome or archoplasm could be 
detected in connection with the sperm nucleus, carried with it great 
weight; but, as it stood a solitary exception to the recent work on 
the subject, criticism was for the greater part suspended until a 
more detailed description had appeared. His completed paper? 
has recently been published, giving additional figures and stronger 
evidence in support of his position. One would have accepted his 
results unhesitatingly, had it not been for the fact that there has 
since appeared a paper? by Kostanecki, who has worked on the 
eggs of the same species, M. g/abrum, and arrived at conclusions 
absolutely at variance with Wheeler’s. ‘This investigator is unable 
to find any persisting egg centrosome, which, he states, utterly 
disappears after the extrusion of the second polar body, but he does 
see a small, clear, archoplasmic area lying close to the side of the 
sperm nucleus, and containing one or two centrosomes and later 
distinct radiations. This sperm aster by division forms the amphi- 
aster of the first cleavage, and the author concludes that Myzostoma 
presents no exception to the view of Boveri. It is unfortunate that 
Kostanecki had not seen Wheeler’s final paper before the publica- 
tion of his own work, as much of his criticism of the latter’s figures 
in the preliminary note is destroyed by the more detailed description 
and by new and clearer figures in the later account. 
In regard to the maturation processes, the two authors are in 
agteement on essential points, but it might be mentioned that Wheeler 
was only able to find a “ Zwischenkérper” in the second polar 
mitosis, while Kostanecki states that he has seen it in the first as 
well, although he does not figure it. 
After the formation of the polar bodies and the two re-formed 
vesicular pronuclei have begun to approach each other, there is a 
_ period when neither Wheeler nor Kostanecki has discovered in many 
1 Journ. Morph., vol. x, No. 1, 1895. 
2 Archiv. de Biol., tome xv, fas. I. 1897. 
8 Archiv. f. mikr. Anat, Bd. li, Heft 3. 1898. 
