140 PROFESSOR E. VAN BENEDEN. 



a series of young in varying stages of development are found 

 on each side of the germ producer, which are more advanced 

 as they are further from the place in which the germs were 

 produced. Side by side with the germs which have arrived 

 at maturity spherical or elliptical bodies with a well-marked 

 longitudinal ortransversestriation are often found (figs. 10-14); 

 they are grouped either in fours or pairs, and are only found 

 near germ producers. These striated bodies, as they are called, 

 were at first taken for spermatophores, but this idea was given 

 up, partly after considering the analogous multiplication of 

 vegetable cells, partly in consequence of the investigations of 

 Biitschli on the multiplication of cells. Prof. Van Beneden has 

 come to the conclusion that this characteristic striation is due 

 to modificationswhich the nucleus undergoes at the moment 

 of cell division. Immediately before division the germ be- 

 comes very granular and opaque, and the nucleus increases 

 considerably in size and its nucleolus disappears; a very 

 clear striation then makes its appearance on the periphery of 

 the nucleus, all the striae meeting at the two poles and run- 

 ning along the meridian of the sphere. A refractive corpuscle 

 then appears at each pole of the nucleus (fig. 10), and very 

 fine granulations collect round each of them. The two poles are 

 then differentiated into a granular polar disc, in Avhich the 

 meridional striai lose themselves (fig. 11). The polar discs then 

 thicken and become more distinct, whilst the strire are not 

 so well marked. Very rarely striated nuclei have been seen 

 in Avhich the fibrillae were a little thicker near the equator 

 than in the rest of their length. The germ has by this time 

 become ellipsoidal, as well as the nucleus, and the polar discs 

 are, so to speak, condensed into two small disc-shaped, re- 

 fractive bodies, the derived pronuclei (fig. 13). Round each 

 of these a clear substance collects from which strise have some- 

 times been seen to radiate ; these are the engendered pronuclei 

 (fig. 13 and 14). Midway between the two derived pronuclei is 

 a granular well-defined plate which is rather thicker towards 

 the centre ; this is the Zellplatte of Strasburger. This forms 

 the plane of fission by which the original cell-plate divides 

 into two, and then each derived pronucleus enlarges and 

 becomes more clearly defined ; * each pronucleus now in- 

 creases in size, whilst at the same time it changes its 

 position, and from being placed excentrically it comes to 

 be in the centre of the daughter-cell; inside it a small 

 nucleolus is visible. The last traces of the clear striated 

 part of the old nucleus then disappears, and Ihe division is 

 complete. The same series of changes is undergone by the 

 daughter-cells, which eventually give rise to a wall-like 



