234 W. WALDEYER. 
the process of fertilization, begun in 1881, were without doubt 
carried on contemporaneously with, and independently of, 
Nussbaum’s work, and the last of Schneider’s. The complete 
work of the latter (Breslau, 1883) is therefore the first 
in order of publication. Nussbaum’s memoir is dated 5th 
August, 1883. E. van Beneden, in 1888, published his 
first contribution on the sexual apparatus of Ascaris megalo- 
cephala in the ‘ Arch. de Biologie,’ vol. iv. Nussbaum’s 
first detailed account appeared in the ‘ Arch. fir mik. Anat.’ 
in February, 1884, and van Beneden’s complete work in April, 
1884. 
E. van Beneden states clearly in the first place that the 
entrance (“la pénétration”’) of the spermatozoon into the eg 
does not represent the act of fertilization. This is effected by 
the perfect maturation of the pronuclei. E. van Beneden 
therefore distinguishes “ Fécondation,” a short definition of 
which we give below, from the “copulation des produits 
sexuelles,”’ by which he means the entrance of the spermatozoon 
into the egg (p. 128, et seq.). 
The characteristic spermatozoon of Ascaris megalo- 
cephala, consists of a protoplasmic portion which is surrounded 
at one end by a membrane, of a peculiar refractive body, and 
of a chromatophilous nuclear-like element, which is surrounded 
by a clear substance in the form of a halo. It is usually, when 
ripe, conical. The thicker end is anterior, and enters the egg 
first, and consists of the chromatophilous body together with 
the halo. The so-called refractive body is placed at the tail end 
of the spermatozoon. 
Now, E. van Beneden maintains that the entrance of the 
spermatozoon into the egg of Ascaris always occurs at a per- 
fectly definite spot. This is characterised by a radially striated 
ton-shaped thickening of the egg-protoplasm (‘disque polaire’’)! 
The middle of this disc presents a roundish hole, through which 
the active, unaltered egg-protoplasm projects from the surface 
of the disc, in the form of a plug (“ bouchon d’impregnation ”’). 
1 Kupffer (120) more recently recognised in the trout’s egg structures 
comparable to the polar disc, but in great numbers. 
