W. Neilson Jones. 
168 
Let us consider fertilization from this point of view and see 
how far the opinion may be justified. Thus regarded, fertilization, 
in all but the most primitive organisms, resolves itself into the 
“ attack” of a “ parasitic ” male gamete upon a female gamete well 
stocked with food reserves. As in cases of parasitism the “ host” 
exercises a chemical attraction upon the “ parasite ” (viz.: the 
male gamete), as a result of which the “ parasite ” cell penetrates 
the “ host ” cell and their respective protoplasms come into direct 
contact with one another. 
In parasitism of the ordinary kind, the destruction of the 
tissues of the host may be rapid and complete—the tissues being 
killed and demolished forthwith. More generally the host cells 
react as to a stimulus, such reaction being expressed by greater 
cell activity, leading in many cases to the formation of warts and 
swellings and other distortions of growth. Stimulation of this 
kind is a common and widespread accompaniment of parasitic 
invasion of tissues, and the hypertrophy or local overgrowth 
which frequently results from it is a well known phenomenon. 
Among vascular plants the numerous cases of gall-formation, 
distortion of growth, or excessive branching leading to the forma¬ 
tion of the so-called “witches brooms” in trees, may be cited as 
familiar examples of such response to invasion of the tissues by 
foreign organisms. Anatomically, swellings of this kind may he 
formed entirely from the tissues of the host, as for instance is the 
case in plant galls produced as the result of oviposition by various 
insects, or they may he of a composite nature, consisting of the 
tissue of the host intermingled with that of the invader, as in the 
nodules formed by many plants as a consequence of invasion of 
the tissues by bacteria or fungi. 
It does not seem unreasonable to regard the growth stimulus 
resulting from fertilization as, essentially, of the same nature. The 
result of the stimulus of fertilization in multicellular organisms is 
the formation of a complex of dividing cells. In unicellular 
organisms, such as Chlamydomonas, a corresponding activity is 
shown, but the individual cells separate as they are formed instead 
of building up a mass of tissue. 
Another well marked characteristic of fertilization is that 
normally the egg-cell is fertilised by one male cell only. The 
behaviour of the sex cells in the brown seaweed Fhcus, studied in 
detail by Farmer and Digby, will serve as an example. 
If an unfertilized egg-cell of Fncns is examined under the 
