MUSEUM OF COMPARATIVE ZOOLOGY. 283 



Salensky ('74", p. 332) mentions the presence of ''ein kugelformigcs 

 Kliimpchen, welches aus den feinsten Kornchen bestand " within tlie 

 germ cell of Amphilina eggs, and is inclined, on the strength of Schnei- 

 der's ('73) discovery, to consider it as the altered germinative vesicle. 



ScHENK ('74, pp. 294-297, Fig. 8) describes the appearance of a clear 

 portion in the middle of the yolk of Serpula, — after the egg has exhib- 

 ited contractile ph-enomena and has eliminated the germinative dot, — 

 which neither occupies the position nor possesses the definite contour of 

 the vanished germinative vesicle. On the contrary, in a radial direction 

 it loses itself in the surrounding protoplasm. This nucleus is not an 

 isolated structure, nor does it differ essentially from the nature of the 

 yolk, save that the yolk granules are there less abundant. Its increase 

 accompanies the gradual disappearance of the space at one time existing 

 between the yolk and its membrane. Sometimes this first nucleus with 

 its radial streaks appears divided into two parts ; this, however, usually 

 occurs only just before the first segmentation. 



Similar stellate nuclei were also seen in vertebrates' eggs. After 

 segmentation it is often seen that one of the resultant spheres con- 

 tains the whole nucleus, w^hile the other only subsequently acquires 

 one, which is formed just as was the nucleus of the first segmenta- 

 tion sphere. Schenk concludes by saying that one sees from this that 

 the nucleus is produced by " a want of uniformity in the distribution 

 of the granular mass," and that the nucleus is to be considered as a 

 central part of the protoplasm, from which it is derived and with which 

 it is intimately united. Subsequently Schenk ('76, Figs. 2 and 4) saw 

 stellate figures in the eggs of Echinus after fecundation, and when the 

 embryo consisted of four segmentation spheres. 



The careful studies of Auerbach ('74, pp. 217-262) on the eggs of 

 Ascaris nigrovenosa and Strongylus auricularis were especially trust- 

 worthy on account of their being continuous observations on living eggs, 

 in which, however, a compressorium was employed. 



After the complete union, near the centre of the egg, of two nuclear 

 structures, which we now know to be like those seen by Biitschli, — the 

 pronuclei, — Auerbach's observations are to the effect that the resultant 

 structure becomes elongated in the direction of the long axis of the egg, 

 and also suffers a reduction of volume. This continues till the structure 

 becomes a very narrow stripe with parallel edges and pointed ends ; then 

 it looks like an exceedingly thin fissure in the protoplasm, and finally 

 disappears ; yet not absolutely without'trace, for during this change the 

 protoplasm surrounding it has become free from granules. Tliis clear 



