48 PROF. A. H. GARROD ON THE MECHANISM [Feb. 6, 
sides of the neck, which render P. rueppelli so easily distinguishable. 
But, in place of the conspicuous white throat and neck which are 
found in both of the previously known birds, the black colour of the 
belly is continued in Plectropterus niger (as I propose to designate 
the present form) up to the chin; and the white colour on the body 
in front is confined to a small space on the mesial line of the lower 
abdomen. The white of the back and scapulars in P. niger has 
also a greenish lustre pervading it which is not observable in the 
other species. This colour passes into a bronzy purple on the wings. 
The size is rather larger than that of our P. gambensis. The bill is 
bright red with the tip whitish, the iris black, the legs and feet of 
a duller red. 
The two specimens received are believed to be both of the male 
sex; they are nearly alike, except that one individual has rather less 
white on the mesial line of the belly than the other. 
In answer to my inquiries, General Cunyngham kindly informs me 
that he received these birds from Zanzibar; so that that part of the 
S.E. African coast is probably the true habitat of this species. 
I will now say a few words as to the distinctness of the two other 
species of the genus (P. gambensis and P. rueppelli), which, though 
admitted, somewhat unwillingly, by Finsch and Hartlaub’, is denied 
by Heuglin?, the most recent authority on East-African ornithology. 
Here, in London, we know full well that the view that P. rueppelli 
is only the adult male of P. gambensis is quite untenable. We have 
had a male of P. gambensis in our Gardens ever since May 1867 
which shows no symptoms whatever of acquiring the frontal knob 
and bare neck of P. rueppelli. In 1864, this bird paired with a 
female of the same species placed in company with it; and the female 
laid eggs, but did not hatch them out. Since then another female, 
received in 1868, has been placed in his company; so that we have 
at present what must be undoubtedly a fully adult pair of P. gam- 
bensis. I will ask any naturalist to compare these birds with the 
example of P. rueppelli (probably a male) obtained from the 
Antwerp Gardens, and most kindly presented to us last summer by 
M. J. M. Cornély, and to say whether it is possible to regard the 
species as otherwise than distinct. 
What De Sousa’s Plectropterus sclateri (Jorn. de Sc. de Lisboa, 
vol. ii. p. 157, 1860) may be, I cannot say. It has certainly nothing 
to do with the P. niger of our Gardens. 
3. On the Mechanism of the Intervertebral Substance, and 
on some Effects of the Erect Position of Man. By A. 
H. Garrop, M.A., Prosector to the Society. 
[Received January 17, 1877.] 
In all works on human anatomy the structure of the disks of 
fibro-elastic tissue which intervene between the bodies of the verte- 
1 Vogel Ost-Afrika’s, p. 801, ? Ornithologie Nord-Ost-Afrika’s, p. 1275. 
