No. I.] VARIATIONS IN LIMULUS POLVPHEMUS. 57 
We assume that there are certain conditions resident in the 
ovum which, under the action of normal surroundings, guide 
it through a long series of changes to the expression of that 
form and mode of action characteristic of what we call the 
normal organism. 
Among the embryos of Limulus, there are some in which 
there appears to be a very slow discharge of vital processes, 
producing the retarded or belated forms ; again, nearly perfect 
individuals are produced within the normal period, but very 
much reduced in size throughout, suggesting the small but 
perfect embryos of Amphioxus that have developed from frag- 
ments of segmenting ova. There are embryos constituting a 
third class, in which a particular charge of formative energy 
was apparently omitted, resulting in the absence of an eye, a 
leg, a neuromere, or a large, definitely circumscribed area of 
the embryo, but without visibly affecting the remaining organs. 
Finally, there is a fourth class, where the embryo seems prop- 
erly loaded and the various charges properly connected, and it 
starts off well, following its normal line of flight for a while. 
But through some inherent defects, the nature of which we can- 
not even conjecture, progressive development ceases at a point 
very far from the mark. Then follows a decline, manifested 
outwardly by a general decrease in size, by fusion and com- 
plete atrophy of one organ after the other, till the whole 
embryo disappears. But as the animal still lives during this 
decline, and in all outward appearances is sound and healthy, 
showing even in the last stages the presence of karyokinetic 
figures, it is obvious that we can only explain this condition 
by assuming that the death rate among the cells is greater 
than the birth rate. And as the last survivors are nothing but 
indifferent, lymphoid cells, we must also assume that the 
gradual approximation of the death to the birth period cuts 
off more and more from the period necessary for cell special- 
ization. The result is a new kind of death for highly organized 
antutals, — one, namely, in which the component cells gradually 
decrease in number and in specialization till nothing remains of a 
once complex organisnt but a few indifferent cells, which in turn 
themselves disappear by a continuation of the same processes. 
