PARTS CONCERNED IN REPRODUCTION. 233 



provisional cell formed by an outgrowth from the walls of 

 the conjugating cells, or is developed without the protec- 

 tion of any extrinsic cell-wall, though after a time it forms 

 one for itself, by the induration of its exterior layer. 



That in many at least of the higher Algae, in which the two 

 combining elements are differentiated into the representa- 

 tives of sexual corpuscules, the germ is at first a mere proto- 

 plasmic mass, would certainly appear from the observations 

 of Pringsheim, which go to show that it is not till after its 

 combination with the phytozoa in the act of impregnation 

 that a cell-wall is formed round it.* There is reason also 

 to believe that the germinal bodies lying within the central 

 cell of the archegonium of the higher Cryptogamia,f and 

 the embryo-sac of the Phanerogamia,J are at first mere pro- 

 toplasmic masses, which only after impregnation form on 

 their exterior a true or distinct cell-wall. 



In animals although in the reproductive organs of the 

 female we have generally two well-marked cells, (the ovum 

 and the germinal vesicle), one within the other, and each 

 with a proper wall, neither seems to be the true homologue 

 of the protoplasmic body of the vegetable, but rather the 

 contents of the innermost that is, the macula or nucleus 

 of the germinal vesicle. Impregnation is effected by the 

 spermatic particles diffusing themselves among the contents 

 of the outer cell or*ovum, either through a special aperture 

 (micropyle) or in some of the other ways noticed before 

 (Chap. III., p. 70) at the same time that the germinal 

 vesicle dissolves and discharges its contents from within 

 into the same cavity, so that the two sexual elements, lying 



* Remarks on the spores of Algae in Rep. of Berlin Academy (Quar- 

 terly Journal of Microsc. Science, IV., 126). Also Braun, Rejuvenes- 

 cence in Nature (Ray Soc. Publ.), p. 156, and seq. 



t So at least they would seem to be in Buxbaumia. See also Prings- 

 heim, as quoted above. 



J Griffith and Henfrey Miscrograph. Dictionary, p. 432. 



