sap or PECK. [Vot. III. 
and in two of the fans used in this work there were only seven 
caudal vertebre actually free, the eighth being imperfectly anchy- 
losed with the end of the coccyx, and in several other ordinary 
birds the same number obtained. No especial reason could be 
given for this increase in the series, since the birds did not 
differ materially from the others in size, nor were any of the 
variations apparently more common in one sex than in the 
other, although two birds with seven vertebrae and one with six 
“vertebrae were male, four with six and the one with five verte- 
bree were female, all having been taken at random from the 
belfry of a church. But the ratio of variation was much greater 
in this lot than is the rule, for in the thirty-odd specimens exam- 
ined, there was no other case of five vertebrze found, and a 
smaller percentage with seven vertebrze would usually be found 
than occurred in this lot of six birds. So also a large white 
male fan with twenty-six tail-feathers was provided with only 
seven actually free vertebra, the same number as an ordinary 
common male bird possessed. But the dissection of such a 
specimen with seven free vertebree shows again that the series 
of nerves is coincident with the series of vertebrze between 
which they are given off, as far backward as to leave only the 
last two spaces without nerves (Fig. 3, si-5s, -%,), adding 
me to fill ss upon the addition of an ss beyond s; The most 
remarkable development of the caudal region is naturally found 
in the fan-tail, since the efforts of selection have been directed 
toward this part of the body in inducing a wide expanse of tail- 
feathering. The usual number of eight vertebrze was found, 
but in two cases the eighth, or last, was imperfectly anchylosed 
to the coccyx, so that although the neural arch was plainly sep- 
arate, yet the body of the vertebra was immovably united with 
the coccyx. A dissection of a specimen with eight actually free 
caudal vertebrz is represented in Fig. 4, where by the further 
addition of another vertebra the intervertebral spaces become 
nine (s;-s5,) in number ; and here too another nerve, ,, appears in 
57, augmenting the series so as to keep z constant with s, ze., 
the last two spaces only in the series of vertebrz are left with- 
out nerves as in the other cases. 
Thus far it will be seen from a series of dissections that the 
supply of nerves from the cord is constant with the series of 
vertebra ; a change in the latter is followed by a corresponding 
