No. 1.] VARIATIONS IN LIMULUS POLYPHEMUS. 97 
be the collapse of the whole, when the working of one part 
is interfered with. Each organism by itself is a world of 
individual cells where heredity, use, disuse, and struggle 
for existence are the determining factors of form and func- 
tion, just as in the larger world organisms as a whole are 
the resultants of these factors. In both cases, sudden and 
great changes in the environment result in a rapid col- 
lapse or death, owing to the impossibility of the cells on the 
one hand, or the organism on the other, adapting themselves 
to the new conditions ; and the result is death of the indi- 
vidual organism in one case, or extermination of the species 
in the other. If the change is a slow one and one calling 
for less specialization, in fewer directions, degeneration, or 
reversion to a simpler plan of structure, may follow till perhaps 
something resembling the original starting-point has been 
reached. 
It 1s an exactly analagous process to this that occurs in some 
of the degenerating embryos of Limulus. It is a new kind of 
death for an individual organism, or, at least, not like the one 
with which we are familar. The embryo, a community of 
thousands of different kinds of cells, does not die like a nation 
swept by a pestilence, or like the starving inmates of a 
helpless vessel, but like a flourishing community in the midst 
of plenty, where some of the infinite niceties of adjustment are 
such as insensibly to reduce the birth rate below the death 
rate, to reduce the complex interrelation of individuals, until 
after many generations the last survivor, reduced to the lowest 
terms, disappears. 
The point we wish especially to emphasize is that in the 
degenerating embryos of Limulus, cell reproduction, cell 
specialization, and cell decay are progressing side by side in 
every part of the body. Karyokinetic figures and the frag- 
ments of decaying nuclei are found side by side. Whether 
the animal develops or degenerates depends on the relative 
intensity of these three factors. The embryos dwindle in size 
because the death rate of the cells is greater than the birth 
rate. The embryo loses nerve centres, sense-organs, and ap- 
pendages because the amount of specialization of individual 
