FUCACE^E . 



with its cytoplasm, while the nucleus alone proceeds toward that of 

 the egg. However, the body which approaches the egg-nucleus is 

 wedge-shaped or narrowed slightly at one end. When the sperm- 

 nucleus reaches that of the egg it is about the size of the nucleolus of 

 the latter (Fig. 30, A). It appears as a densely stained and somewhat 

 flattened or lens-shaped body closely applied to the egg-nucleus (Fig. 

 30, B). An increase in size now follows, during which the denser 

 appearance gives way to that of a less compact structure (Fig. 30, C). 

 It is now seen (Strasburger, '97, p. 364) that the sperm-nucleus 

 possesses a thread-like framework. With further increase in size the 



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FIG. 30. Fecundation in Fucus. A-D, Fucus vesiculosus. E, .F. serratus . (After Strasburger.) 



A, Egg-cell ten minutes after mixing of sexual elements ; male nucleus applied to that of egg. 



B, same two nuclei more highly magnified. 



C, similar to B ; sperm nucleus lies between the observer and egg-nucleus. 



D, fusion of nuclei has progressed further ; 10 minutes after mixing of sexual elements. 



E, i% days after fecundation; fusion nucleus preparing for division; poles of future spindle present, 



but limits of the two nuclei still recognizable ; the part derived from male nucleus (on the left) has also 

 a nucleolus. 



chromatin thread becomes more prominent, and the boundary between 

 sperm and egg-nucleus gradually disappears (Fig. 30, D, E). In the 

 meantime a nucleolus is found in that portion of the fusion-nucleus 

 coming fi-om the sperm. This is in all probability not brought in 

 as such, but is developed during the process of fusion much in the 

 same - way as in the reconstruction of daughter-nuclei following karyo- 

 kinesis. 



In no case observed by the authors mentioned was the sperm-nucleus 

 accompanied by a centrosphere or a system of radiations, either during 

 its passage through the cytoplasm or during fusion. Strasburger ('97, 

 p. 365) states, however, that in some cases he was able to trace the 

 apparent connection between the two centrospheres and the limits of 

 the two sexual nuclei in the oospore (Fig. 30, E), and he infers that 

 the centrosomes may have been brought into the egg by the sperm in 



