FUCUS SERRATUS 405 



present in considerable numbers, they give to the 

 ova an irregular rotating movement. 



Actual coalescence of tlie spermatozoid with the ovum is 

 difficult to observe : the appearance of a second nucleus in the 

 ovum has, however, been described, and its coalescence with the 

 nucleus of the ovum : it is probable that if a spermatozoid, as 

 such, enters the ovum, its entry is very rapid. 



XII. The most satisfactory way of tracing the de- 

 velopment subsequently to fertilization is by artificial 

 cultivation : this has been done by Rostafinsky, 

 so as to prove that the fertilized ovum develops 

 directly into the Fucus plant ; but the cultures, being 

 difficult to carry out, are not fitted for class demonstra- 

 tion. It is thought that the following simple observa- 

 tions will suffice. 



On stones, in districts where Fucus abounds, there 

 may be found in early summer olive-brown velvety 

 patches : on examining these with a lens, small club- 

 shaped bodies may be distinguished, attached by their 

 narrower end to the substratum, and with their 

 broader, free end crowned by a tuft of hairs: these are 

 young plants of Fucus, or of one of the allied genera. 



Having collected such material, and treated it as 

 above directed, tease it out with needles, in glycerine, 

 and examine the plants thus separated under a low 

 power : the following points are the most worthy of 

 note 



1. The nearly spherical form of the very young 

 plants, which consist of but one, or of relatively few 

 cells, and are limited externally by a definite cell- wall, 



