366 Ewartr— Variation: Germinal and Environmental. 
a portion and then the whole of the hybrid larve from the Spheerechinus to tts own type. 
In other words, the characteristics of the hybrid offspring depend directly on the relative 
degrees of maturity of the sexual products.””* 
(5). Why members of a family differ. 
To return to the question, ‘‘ Why is there sometimes so much difference between 
the individual members of a family ?” it may be replied, that the individuals differ 
because the cells from which they are respectively developed differ; the potential 
difference of the cells bemg greater than the actual difference of the individuals 
derived from them. Hence, an attempt to account for the difference between mem- 
bers of the same family does not consist in studying selection or the changes that 
accompany conjugation. It resolves itself into an attempt to explain in what respects 
the cells from which the offspring are separately and independently developed differ 
from each other. It is conceivable that the individual germ-cells entering into the 
formation of any given family may differ both morphologically and physiologically. 
Each germ-cell, up to a certain point, may be said to be comparable to a simple 
protozoon. Each protozoon, however simple, and though only capable of repro- 
ducing itself by fission, has a life-history. The life-history begins at the moment 
of separation and ends when the process of fusion or conjugation sets in. This 
may be very short or relatively long; but, however short, there will be time for 
complex metabolic changes, for minute fluctuations in its vital units. The protozoon 
may be well or ill-nourished ; 1t may have matured (¢.e., become capable of dividing) 
rapidly or slowly; it may divide prematurely, or the process of fission may be 
delayed, and, when fission does occur, there may be unequal division of the 
nucleus. 
In the case of the female germ-cell three stages may be recognised in the 
life-history—(1) the stage up to the discharge of the first polar body ; (2) the 
stage characterised by the extrusion of the second polar body ; and (3) the stage 
between the reducing division and the union of the nuclei of the ovum and the 
spermatozoon—~z.e. up to the moment of conjugation. During the first stage the 
ovum, like a protozoon, may be ill- or well-nourished, the growth may be fast or 
slow throughout, or, by sudden changes in temperature, &c., rapid at one time, 
retarded at another, or slow at first and so hurried at the end that ovulation takes 
places prematurely. Moreover, if only one or two ova are ripening in, say, the 
right ovary, and quite a number in the left, the right ones may have the advan- 
tage and some of those in the left may be inadequately nourished, just as ova, 
* Proceed. Roy. Soc., vol. lxiii., May, 1898. 
