APPROACH AXD CONJUGATION OF THE NUCLEI, ETC. 17 



divides into two, thus giving rise to a tetraster or quadruple aster such as is shown in Phototype 22, Plate VI. 

 The eggs thus double-fertilized divide into four (instead of two) at the first cleavage, and the entire cleavao-e is 

 double, as if the egg consisted of two embryos joined together. They give rise to a blastula stage, apparently 

 normal, but, as Driesch has shown, a gastrula is never jDroduced, and the embryos die without attaining maturity. 



Plate IV. Phototype 13. 

 Groivth of the Aster. 

 A stage slightly later than No. 1 1 showing the growth of the aster (4 minutes after entrance). 



Plate IV. Phototype 14. 



Approach of the Nuclei. 



Later stage, 5 minutes after entrance, showing the remains of the entrance-cone and the sperm-head completely 

 rotated and approaching the egg-nucleus preceded by the aster (cf. Text-fig. XI. A). The central mass (centrosphere) 

 shows with extreme clearness in the preparation. Its boundary is irregular, its substance finely granular without 

 indication of any centriole. In preparations of this period double stained with hcematoxylin (blue) and Congo red 

 the astral rays appear blue, while the central mass has a purplish or reddish tone. 



Plate IV. Phototype 15. 



The Sperm-aster at a Maximum {y minutes). 



The focus is here sharply on some of the astral rays, which are shown with especial clearness, while both 

 the nuclei are slightly out of focus. Many important details of the astral structures are shown. The rays are 

 long, conspicuous fibres, having a wavy course and composed of rows of microsomes which stain bright blue in 

 ha^matoxylin. This is especially ajaparent in the outer portions of the rays where they run out into rows of granules 

 indistinguishable from those of the general reticulum into which the rays break up. Passing inward toward the 

 centre of the aster, the microsomal structure of the rays becomes less apparent, and they finally fuse indistinguishably 

 to form the central mass, which has an ill-defined contour and a finely granular or nearly homogeneous structure. 

 In sections double stained with iron hematoxylin and Congo red or acid fuchsin the astral rays appear intensely 

 blue, while the central mass is red or purple like the original middle-piece, although somewhat obscured by the 

 surrounding blue structure. This contrast between the red central mass and the blue rays becomes extremely 

 conspicuous in later stages, and is described further on. The sperm-nucleus at this period is slightly enlarged, and 

 as a rule has lost its lance-shaped outline. 



