SOME PROBLEMS OF REPRODUCTION. 593 



'^ fertilised egg" ^ of the Rotifer, the Green-fly, and the 

 Eutomostracan (in marked contrast to the parthenogenetic 

 egg, which develops at once), after a few segmentations, 

 passes into a state of rest, to germinate only after a prolonged 

 rest. The same holds good with the seed of most flowering 

 plants, as I know to my cost, being a raiser of Abutilons ; 

 the germ forms an embryo of many similar cells, whose 

 development is arrested after a time. Then, only after a 

 lapse of months, it may be, when exposed to suitable con- 

 ditions — heat, moisture, and aeration, — it starts to grow. The 

 same applies to tubers and statoblasts. 



If now instead of counting species of living beings we 

 count types of reproduction, which are so varied in the 

 Protista, the Algfe, and the Fungi, we shall find that in the 

 majority of cases the pairing-cells are naked, but that the 

 fusion-cell immediately invests itself with a complete wall, 

 anxi either goes to rest itself, or, as in most Sporozoa, divides 

 into a limited number of cells, which themselves pass into the 

 resting state. Indeed, the almost universal formation of a 

 cell- wall around the fusion- cell or oosperm, as soon as the 

 process of fusion takes place in Metazoa and in Metaphytes 

 may be regarded as a survival of this tendency of the cell 

 formed by the fusion of two to pass at once into rest (see 

 below, p. 607). Had our knowledge of reproductive pro- 

 cesses been derived from these lower beings, we should never 

 have associated the gemnination of the resting-cell with the 

 process of cell-fusion. 



The word " fertilisation " labours under two disadvantages 

 in its later actual sense, which, historical considerations not- 

 withstanding, must to-day be regarded as its correct sense : 

 (1) in the minds of most naturalists it is still tainted with 

 the idea of wliat we have differentiated as *' germination " — 



1 The term eg^ denotes four cells morphologically distinct: (1) the ovarian 

 egg; (2) its daughter, the sister-cell to the first polar body; (3) the "matured 

 egg," sister to the second polar body and daughter of (2) ; (4) the " fertilised 

 egg," or oosperm. But, as all four are nearly identical in size and cytoplasm, 

 it is convenient to retain the word "egg" to denote them indifferently. 



