JuLy 3, 1902] 
we must look for tests of intellectual efficiency.” Not the least 
interesting paper at the present time is Dr. W. R. Macdonell’s 
note on the result of previous vaccination on the effect of small- 
pox when incurred. According to the abstract “ he shows that 
the correlation of foveation and size of scar with severity of 
attack is only moderate, but that there is very considerable cor- 
relation indeed in all the recent epidemics, not only between 
recovery from, but between the severity of the attack and the 
existence of the scar.” It has not hitherto been found possible 
to obtain statistical data for deducing the correlation between 
the presence of the scar and the habit of life of the persons 
attacked. To the miscellanea Mr. Yule contributes a note on 
local death rates. It is evident from this synopsis that the 
standard of the publication is being well maintained and that 
the new biometric methods are capable of extension over the 
most diverse fields of biological science. 
AVIAN ORGANOGENY.' 
R. MITCHELL has already devoted considerable attention 
to the study of the intestinal tract of birds, and in the 
present contribution he gives us the results of his latest re- 
searches, which have embraced all orders of birds and many of 
the smaller groups. 
Adopting the method of investigation pursued by Cuvier, the 
intestinal tract is removed from the body by severance at the 
plyorus and the cloaca, and along the mesentery close to the 
body-wall. Next, the cut ends of the gut are pinned down and 
its coils unravelled, until they stand revealed as a corrugated tube 
suspended by the ventral edge of the mesentery. 
In tracts so displayed, Dr. Mitchell recognises three distinct 
loops, a duodenal, a rectal, and a large loop lying between 
these two which he calls Meckel’s tract. The comparison of 
the varied forms which these loops take constitutes the subject 
of Dr. Mitchell’s researches. 
Evolution is rightly the key-note of this work, and accord- 
ingly the author starts with a detailed description of what he 
regards as the most primitive type of gut, from which all others 
have been derived. This type—found not, as one might have 
expected, in one of the Ratitze, but in the ancient goose-like 
bird, Palamedea—he calls the archecentric type, whilst modified 
conditions thereof are distinguished as apocentric. Three kinds 
of apocentricity are recognised—multiradial, uniradial and 
pseudocentric. Multiradial apocentricities are those which are 
purely adaptive or homoplastic, and accordingly are of no value 
as indications of kinship, since they may, and do, occur re- 
peatedly and independently in different groups. Uniradial 
apocentricities, on the other hand, Dr. Mitchell defines as 
complex modifications ‘‘of a kind that we cannot well expect 
to be repeated independently, and. . . . must be the most certain 
guides to affinity.” 
Not seldom a uniradial apocentricity will form a new centre 
around which new diverging modifications are produced, and 
such centres he proposes to call metacentric. 
Pseudocentric apocentricity appears to be extremely common 
and very difficult to distinguish froin the archecentric condition. 
Generally, however, its secondary nature is revealed by some 
small and apparently meaningless complexity. 
The valuation and nomenclature of these characters form a 
special section of Dr. Mitchell’s paper. It is extremely suggestive, 
and will be read with interest by many whoare not directly inter- 
ested in avian morphology. 
The systematic description, which follows this discussion, 
occupies the bulk of the paper, the intestinal tract of every 
order of birds being reviewed, copious illustrations serving to 
bring out, not only the very striking modifications which have 
taken place, but also the difficulty of the work undertaken. 
Space forbids us dwelling, as we would fain do, on this sec- 
tion and the summary thereof at greater length. Suffice it to 
say that the very remarkable modifications of these loops, 
which Dr. Mitchell has brought to light, are extremely inter- 
esting and very suggestive. We venture to doubt whether a 
good case has been made out for the position, near the Ralline 
forms, which has been assigned to the Tinamous. Markedly 
apocentric though they may be in the matter of their intestinal 
1 “On the Intestinal Tract of Birds: with Remarks on the Valuation 
and Nomenclature of Zoological Characters.” By P. Chalmers Mitchell, 
M.A., D.Sc. (vans. Linn. Soc., vol. viii. part vil. rgor.) 
NO. 1705, VOL. 66] 
NATURE 
nae 
2735 
v 
coils, yet we see no reason why they should not be allowed to 
remain among or very near the Ratitz. | 
The concluding section, on ‘‘ Characters and Classification,’ 
forms a most admirable summary. ‘‘ In the systematic descrip- 
tive part,” the author writes, ‘‘ my task was to treat the charac- 
ters of the patterns displayed by different birds as nearly as 
possible as if the gut were the whole animal, and the various 
phylogenetic figures and the three plates display what I take to 
be the relations of the intestinal tracts, and not necessarily the 
relations of the possessors of these tracts. I have been taking, 
in fact, the anatomical structure as the unit, and not the indi- 
vidual or the species. . . . Granting that the plates attached to 
this paper represent with approximate accuracy the phylogeny 
of the intestinal tract in birds, we have yet to learn the relation 
of the phylogenetic tree of this structure to the phylogenetic 
trees of other structures, and the relation of all these to the 
phylogenetic trees of those impermanent combinations of charac- 
ters which we call species.” 
We would fain quote more of this interesting section, but 
enough has, we trust, been set down here to draw the attention 
of morphologists generally to a contribution which is at once 
valuable and suggestive, and likely to remain the standard 
work of reference on this subject for some years to come. 
WP. PB: 
RPHOROGRAPHY AS VAPPETED RAO 
ARCHITECTURAL MEASUREMENT AND 
SURVE YING.1 
WHILE the impressions which a photographic picture yields 
to a casual observer may or may not be correct, the rela- 
tionship which exists between a photograph and the objects the 
images of which are depicted is always definite, and a little careful 
attention in arranging the conditions under which a picture is 
taken will suffice to make easy the correct interpretation of it. 
To understand the geometric nature of a photograph it must 
be noted and always remembered that for practical purposes a 
photograph is a surface of two dimensions, which for choice 
should be a plane surface, and it is only possible to obtain by 
photography exact copies of similar object surfaces, and these 
only when the surfaces to be copied are exactly parallel to the 
picture surface. 
Under these conditions written or printed documents or 
drawings can be, and often are, copied by photography, so as to 
be practically exact copies of the originals. The copies may be 
the same size, or larger or smaller, but all proportionate 
dimensions will be the same, whatever the relative sizes of 
object and image may be. : 
To illustrate the first elementary principles of the subject a 
photographic picture of straight lines and right angles, arranged 
to form a set of regular squares, was projected on a movable 
screen. It was shown how, when the screen was parallel to the 
lantern slide, there was no perceptible bending of the lines and 
no perceptible enlargement or diminution of any of the angles, 
from which it might be concluded that there could have been no 
perceptible distortion in any part of the picture. By moving 
the screen nearer to, and further from, the lantern, it could be 
seen that while the forms of the squares remained constant their 
areas varied with the distance, in obedience to the ordinary 
laws of rectilinear radiation, from a point, and it was shown 
how a photographic picture may be legitimately regarded as 
being made up of a number of points, each one of which is at 
the picture end of a straight line, which may be taken for prac- 
tical purposes to have travelled from a corresponding object 
point through a station point at the apex of a cone of rays 
radiating towards the picture. 
The geometric relationship between distant objects and photo- 
graphic images of those objects can be most easily appreciated if 
the lens is supposed to be replaced by a pinhole at the station 
point, when it is evident that a straight line from any point of 
the image to the pinhole will, if prolonged, pass through the 
corresponding object point, and vice versd. Thus any number 
of true direction lines can be obtained at will. 
For making plans, these direction lines can be projected as 
horizontal rays on a ground plane as in plane table surveying, 
and positions can be fixed on the plan by the intersection of 
1 Abstract of a paper, by Mr. J. Bridges Lee, read before the Society of 
Arts on April 16. 
