SECT. I 



MORPHOLOGY 



93 



cell body, a nucleus, and the rudiments of chromatophores are always 

 present in the egg. The sper- 

 matozoid (Fig. 99), on the otlier 

 hand, becomes transformed, in 

 the more extreme cases, into a 

 spirally twisted body, provided 

 with cilia, and exhibiting an ap- 

 parently homogeneous structure. 

 Only a knowledge of the history 

 of its development, and the great- 



est care in fixing and 



staining, 



have rendered it possible to recog- 

 nise the homology of the structure 

 of such a spermatozoid with that 

 of an embryonic cell. It has been 

 shown that the hinder part of its 

 spiral body corresponds to the cell 

 nucleus (/i), the anterior, together 

 with the cilia, to the cytoplasm, 

 especially the kinoplasm (c), and 

 the vesicle {h), at the other ex- 

 tremity, to the sap cavity of a 

 cell (88). 



Motile male cells provided 

 with cilia, occur only in the 

 Cryptogams and, as has been 

 recently demonstrated (^^), in 

 some Gymnosperms (Cycadaceae, 

 Ginkgo). In the Cryptogams the 

 spermatozoids are set free from 

 the sexual organs and require 

 water for their dispersal. They 

 reach the egg-cell, which usually 

 remains in its place of origin, 

 by swimming. In the Gymno- 

 sperms, which form motile sperma- 

 tozoids, the latter are brought 

 near to the ovum by means of the 

 pollen tube developed from the 

 pollen grain. In a similar way 

 the non-motile male cells of the 

 other Gymnosperms and the Angio- 

 sperms are conducted to the egg 

 through the pollen tube (Fis. 



,rH- 



FiG. 100. Fertilisation in an Angiospermic 

 phanerogamic plant. Somewhat diagraniatic. 

 A. End of the pollen tube containing sk the 

 generative or spenn-nuclei, r/c the vegetative 

 nucleus, which later breaks down. B. Upper 

 end of an embryo-sac with the entering end of 

 the pollen tube, e egg, elc, egg-nucleus ; ch, 

 rudiments of the chromatophores ; syn, syner- 

 gidae ; snlc, nucleus of the synergidae ; ew, wall 

 of the embryo-sac ; C and D, eggs in succes- 

 sive stages of fertilisation, sk, sperm-nucleus ; 

 syn*, the synergid that received the contents of 

 the pollen tube, sk, sperm-nucleus ; ek, egg- 

 nucleus. In D these are uniting to form the 

 nucleus of the embryo, (x about 500.) 



100). In the union of the two 



sexual cells in the act of fertilisation, the egg nucleus (e/j) and the 



