No. 2.] THE STUDY OF VARIATION. 459 
In the first block of twenty specimens the average number 
of vertebrze for each animal is 45.7. The sum of the depart- 
ures from this mean in sixteen normal specimens is 22.4, giving 
in this block an average departure from the mean, for each 
specimen having the pelvis on the XIX vertebra, of 1.4. The 
four homeceotic specimens, however, show an average departure 
of 1.6, z.¢., the amplitude of variation among the homeceotic 
specimens is greater. The second, third, and fourth groups of 
twenty also reveal greater amplitude of variation on the part 
of homeeotic individuals, though the last group is exceptional, 
the homceotic specimens showing less variation than the nor- 
mal. The tabulated results are as follows: 
The mean amplitude of meristic variation of the normal specimens 
In the first 20 is 1.4 and of the homeotic specimens is 1.60. 
In the'second'20) * 94 “ “ « a ¢ SOP sO i): 
Imbthethirdy2oy 61.35, sees <c cs SiGe 
inthe fourthy2o, 6 1.52) < <6) <6 ‘ “ Ge Gigs. 
Imbtheffthy2o) es o1:66) 66 <6 ise Ke ‘ 5 inate, 
In I00 oete37e “call the i ss STO. 
Though in this table there is considerable irregularity in 
the ratios, it seems to the writer that the final figures, 1.37 and 
1.61, are sufficient to warrant the conclusion that specimens 
having abnormally placed sacra (homeceotic) do present a con- 
siderably increased meristic variation, and aside from the fact 
that there are twice as many homeeotic specimens on the right 
as on the left of Plate C. 
Is the converse true? Do specimens presenting extremes 
in meristic vertebral variation tend towards homeeosis ? 
An examination of the facts in the case brings out most 
striking results. There are only two specimens whose 
vertebree are reduced to the abnormal number of forty- 
three, and both of these are homeeotic. Of the nine 
examples bearing forty-four vertebre, only 33% are home- 
otic. Of the twenty-one specimens bearing forty-five verte- 
bree, only 19% are homceotic. As the vertebrae now leave 
the normal and tend towards the other extreme, homceosis 
becomes more frequent, as will be observed by reference to 
the table. 
