108 
speaking, the term gastrulation should only be 
used of forms in which an undoubted gastrula 
has been shown to be present; to use it in refer- 
ence to the two-layered condition of a bird or 
mammal in which there is the greatest reason to 
doubt that a true gastrula stage exists at all, is 
simply to court confusion, and leads to such 
absurdities as the statement that “endoderm,” or 
“ectoderm,” is not homologous throughout the 
series of vertebrates. To give a cell-layer, the 
name endoderm in the various types of verte- 
brates is, of course, merely a short way of stating 
that it is homologous in these various types ! 
(3) Dr. Levy’s book affords a short sketch of 
vertebrate embryology written from a_ practical 
point of view. Simple instructions as to labora- 
tory methods are given, stress being. very properly 
laid on the preparation of thick, free-hand_ sec- 
tions of embryos—the great instructiveness of 
which is too often ignored. The chapter on tech- 
nique is followed by an account of gametes and 
gametogenesis, then by chapters on early develop- 
ment in amphibia and in the chick, while the 
remaining half of the book is devoted to organ- 
ogeny and a short chapter on developmental 
mechanics. 
OUR BOOKSHELF, 
The Change in the Climate and its Cause. By 
Major R. A. Marriott. Pp. 94. (London: E. 
Marlborough ‘and Co:, n.d.) Price 1s. 6d; 
cloth’ 25,6: 
Tuis book is a contribution to the great Drayson 
Myth, and as such it may appeal to those with 
whom it is a fair presumption that any theory of 
orthodox science is wrong, and also to those who 
take a curious interest in the vagaries of that class 
of mind. 
Major Marriott, ‘like ‘Sir Ay tdevHorseyy in 
“Draysonia,” complains that Drayson was not 
taken seriously. The fact is perfectly true, but 
the complaint is unjust precisely because General 
Drayson (not without professional precedents) 
failed to take seriously the position he was assail- 
ing. Astronomy is unique among sciences in its 
dependence on a_ single controlling principle, 
gravitation. It is open to anybody to abolish that 
principle and coordinate the facts otherwise—if 
he can. Or he may question the accuracy in 
detail of a mathematical deduction or demonstrate 
a false assumption. What he cannot do is to 
isolate a piece of the whole doctrine, reject the 
operation of the general law in the particular case 
on insufficient grounds, and ignore the effect of 
what he is doing on the whole related theory. 
It would be unprofitable to comment on 
the errors (as we deem them) of the present 
work. It is pleasanter to mention the one per- 
tinent remark which we have come across. This 
is the reference to the theory of “planetary 
inversion” (p. 66). It is quite possible that tidal 
NO. 2318; VOL. 193] 
NATURE 
[APRIL 2: rer 
friction is slowly changing the obliquity of the 
ecliptic, and thus exercising a secular influence on 
climate. But the effect is very slow; it is not 
periodic; and there is little in common between 
the methods of Mr. Stratton and those of General 
Drayson and his followers. 
The book deals largely with changing climatic 
conditions, the evidence of geology, and the bear- 
ing of the so-called astronomical theory of an ice 
age. But why are the possibilities limited by 
the tacit assumption that the radiation of the sun 
has been constant through geological ages, an 
assumption not merely unproved, but even im- 
probable ? | Reed Oe Fs 
Perspective made Easy by Means of Stereoscopic 
Diagrams. By C. E. Benham. (Colchester : 
C. E. Benham, 28 Wellesley Road.) Price 
(post free) 6s. 2d. 
Tuis set of fifteen stereograms is intended as a 
substitute for models as used by teachers and 
students in illustration of some cf the rules and 
principles of perspective projection. When 
viewed in a stereoscope the diagrams exhibit in 
relief, amongst other things, the principle of the 
convergence or parallelism of the projections of 
parallel lines in space; and the rotation into the 
picture plane of horizontal and vertical vanishing 
planes, thus illuminating the constructions relat- 
ing to vanishing and measuring points for hori- 
zontal and inclined lines. An explanation is given 
in a sixteen-page pamphlet which accompanies 
the stereograms. 
The idea of the author is good, but it is not 
very efficiently carried out. The views are not 
always so convincing as they might be, and the 
descriptions are occasionally lacking in mathe- 
matical precision. We also think that the price 
has been fixed too high. Nevertheless, a teacher 
would receive some useful suggestions by a study 
of the diagrams. 
A Laboratory Manual of Organic Chemistry for 
Beginners. By Prof. A. F. Holleman. Edited 
by Dr. A. J. Walker. Second edition; pauihy 
re-written. Pp. xvii+83. (New York: John 
Wiley and Sons; London: Chapman and Hall, 
Ltd., 1913.) Prices4s> 6dsnet: 
A REVIEW of the first edition of Dr. Walker’s 
translation of Prof. Holleman’s little book ap- 
peared in the issue of Nature for May 11, 1905 
(vol. Ixxii., p. 28). New experiments have been 
incorporated in the present edition, and some 
obsolete reactions have been omitted. 
Engineering Workshop Exercises. By Ernest 
Pull. Pp. viii+80. (London: Whittaker and 
Cos, m914:)- Price 25-7 ner 
Tuis little book provides instructions to enable 
technical students and apprentice engineers to 
perform their workshop experiments and exercises 
intelligently, and to obtain practice in the use of 
ordinary engineering tools and appliances.  Pro- 
minence is given to the value of working draw- 
ings, and accuracy is insisted upon consistently. 
A chapter on screw-cutting and notes on materials 
are included in the book. 
