No. 1.] VARIATIONS IN LIMULUS POLYPHEMUS. 51 
phenomena, antithetical to the associated phenomena of degen- 
eration, specialization, and lack of regenerative power. 
We have thus seen how differences in the time and place of 
growth will in normal embryos produce conditions that cause 
the fusion and degeneration of organs. 
In such cases the fusion and degeneration took place in front 
of or behind the true extremities of the body. But we see no 
reason why the same kind of factors should not produce the 
more extensive median fusion and degeneration seen in the 
abnormal forms. 
This supposition becomes all the more plausible when we 
consider that the lines of fusion and degeneration are coinci- 
dent with the lines of greatest stress. 
Again, we can see how reversing the conditions that have 
brought about median fusion and degeneration, z.e. diminished 
lateral cell stress at the anterior end, might permit the forma- 
tion of double and triple monsters, — as shown by Fig. 7, p. 73. 
And finally, if the half-metameres were very much reduced 
in numbers, the tendency to increase in width at the lateral 
end would have greater freedom, and more or less ovoid bodies 
would result, in which the segmentation would be lost sight of 
in the antero-posterior expansion of the half-metameres. The 
organs would then tend to be formed along concentric circles, 
somewhat as in the embryo of a cephalopod. 
Having considered what we have regarded as the general 
principles involved in this class of variations, we will now 
examine the individual illustrations of the same. 
An early stage of fusion is well shown in Pl. V, Fig. 39. 
The cephalic lobes are constricted, and without character. 
The chelicerae are absent. The next two appendages are 
brought closely together, but the space between the appendages 
of the following pairs becomes greater, till in the last thoracic 
metamere they are separated from each other by the normal 
distance. 
A tendency in the same direction is seen in Fig. 47, as is 
shown by the mere trace of cephalic lobes, the absence of 
