226 W. WALDEYER. 
doubtful whether in all cases there is no relation between the 
entrance of the spermatozoon and the extrusion of the directive 
corpuscles, since Kupffer and Bohm (81) have shown in the lam- 
prey that one directive corpuscle is extruded before, and the 
second immediately after the entrance of the spermatozoon. 
In Ascaris megalocephala, both are extruded after the 
entrance of the spermatozoon (H. van Beneden). 
Before Fr. Miller, K. E. von Baer, and then Dumortier, P. J. van Beneden, 
and Kolliker had recognised directive corpuscles in Mollusca (cf. the quota- 
tions in Mark’s work, No. 181).} 
Dumortier and P. J. van Beneden observed in Limneus and in Limax 
two corpuscles pass out of the egg; Kolliker saw three in Doris; this third 
one was also seen by Trinchese, Blochmann, and Platner (160), in Mollusca. 
This is due to the fact that of the two originally formed bodies one divides 
into two. Von Baer regarded the small body seen by him in Anodon pro- 
jecting from the yolk like a small hillock, below the yolk-membrane, as the 
whole of the germinal vesicle. Dumortier and P. J. van Beneden looked on 
their corpuscles as the offspring of the germinal vesicle. In Mammals, 
Barry and Bischoff were the first to observe these corpuscles, but without 
clearly recognising their significance. Bischoff inclines to Loven’s explanation, 
that they are the extruded germinal spot. E. van Beneden, in his above- 
mentioned work (18), gave further figures of the process in Mammals 
(Vespertilio murinus and Lepus cuniculus). His figure shows small 
nuclear-like structures in the bladder like corpuscles. HE. van Beneden gave 
to them Robin’s name of “ Vésicules s. globules polaires.” Rathke (167), 
at the same time as Fr. Miiller and in the same place, mentioned the directive 
corpuscles and denied any particular meaning for them: they are droplets of 
yolk-substance, which are expelled from the latter through its contraction. 
Oellacher convinced himself that the whole nucleus (germinal vesicle) was 
extruded in the Fowl and Trout, and that this extruded nucleus represented 
the directive corpuscles. Purkinje (164), von Baer (as already mentioned), 
Wagner (200), Bischoff (27, 28), Coste (50-52), and Allen Thomson (197) 
had already recognised that in fully ripe eggs the germinal vesicle moved 
towards the surface and disappeared, but they did not explain how it came 
to disappear. Many workers, e.g. A van Bambeke (11), have held the view 
that the substance of the germinal vesicle is distributed temporarily in the 
1 Robin (1. c.) and Platner (‘ Arch. f. mik. Anat.,’ Bd. xvii) quote Carus, 
who, in 1828, discovered the directive corpuscles,—‘ Bull. de Férussac,’ Paris, 
t. xiv, p. 182—* Sur la rotation de ’embryon dans l’ceuf des Mollusques 
Gastéropodes ;” but Platuer leaves it doubtful whether the discovery really 
belongs to him. I have been unable to obtain the memoir. 
