_ APRIL 29, 1897 | 
NATURE 
619 
general effect combined with considerable differences of detail, 
and by the process of ‘‘ projection” these differences of detail 
may be exaggerated while the general similarity is obscured. 
While accepting Fritz Miiller’s expianation of the mimicry of 
protected species by each other, and as also affording the only 
intelligible reason for there being only two types of colour- 
pattern in the whole 400 species of the Danaoid Heliconide, he 
says that ‘‘unfortunately no dzvect experiments have been made 
on the feeding habits of young South American birds.” But in 
view of the careful experiments of Prof. Lloyd Morgan on a 
variety of young birds this is hardly necessary, as it is proved 
that they have in no case any instinctive knowledge of what is 
edible or distasteful, while they acquire the knowledge by ex- 
perience with extreme rapidity. Like many other writers on 
the subject who have recently criticised and rejected the theory 
of warning colours as indicating inedibility, Mr. Mayer does 
not distinguish between the /adztwal and the only occastonal 
enemies of protected insects. Thus he refers to the experiments 
of Beddard, showing that toads will eat any insects whatever ; 
but it is quite certain that toads are not very dangerous enemies 
to either butterflies or their larvae, nor probably are marmosets, 
which are also general feeders. There is quite sufficient evidence 
to show that insects with warning colours ave rejected by most 
insectivorous birds and lizards, which are certainly the most 
general and most dangerous devourers of insects both in the 
larva and winged state, and these facts, taken in conjunction 
with the experiments of Prof. Lloyd Morgan, afford a firm 
foundation for the whole theory of warning colours and 
mimicry. ANN. VV. 
THE PRIMATE BRAIN} 
THE comparative study of the convolutions of the brain sur- 
face in man, apes and monkeys, may be said to have been 
founded by Gratiolet, who mapped out the fissures in the lower 
monkeys, traced the patterns upwards through the apes to man, 
and invented a system of names for the convolutions. In recent 
years this study has received impulse from two distinct causes : 
on the one hand, the greater opportunity of examining the 
brains of the higher apes; and, on the other, the attempt to 
locate in the convolutions definite functions has led to experi- 
ments being conducted, by physiologists and psychologists, upon 
the brains of monkeys. A great variation in the conyolutions of 
species of monkeys and of apes has been thereby shown to exist, 
and more accurate data have been rendered available for a true 
morphological comparison with those of man ; and although the 
subject has, toa very great extent, been attacked from a physio- 
logical standpoint, yet the morphology of the convolutions has 
received increased attention during the past few years, notably 
at the hands of Dr. Cunningham, whose careful and extended 
work on this subject covers a good deal of the ground opened 
up in the present memoir, which deserves a place alongside that 
of the Dublin anatomist. 
The publication of Dr. Parker’s work, which was communi- 
cated verbally, to the Academy of Philadelphia, as long ago as 
1890, has been delayed till last year, owing to a variety of cir- 
cumstances—amonegst others, the death of the author in 1892. 
After an introduction dealing with the scope and aim of the 
memoir, there follows an interesting historical survey of the ob- 
servations and opinions of the chief writers on the subject. The 
author then tabulates the names of the fissures and convolutions 
applied to the human brain, with their synonyms as employed 
by each author. This table will be of considerable value to 
students of the subject, as will be the historical survey. 
How are these convolutions and furrows on the surface of the 
brain brought about ? What is the cause of the gyrencephalous 
condition ? This is stilla matter of controversy. To this question 
two chief, but opposing answers have been suggested, each sup- 
ported by equally competent authorities. The one school looks on 
these convolutions as due to the effect of pressure of the slowly 
growing skull on the more rapidly growing brain. The opposite 
school believe the cause to be innate—that is to say, the convo- 
lutions owe their origin to differential growth in certain 
definite regions of the brain surface itself. Dr. Parker combines 
these two opposing views: believing that certain ‘‘ fundamental 
1 * Morphology of the Cerebral Convolutions, with special reference to 
the Order of Primates.” By Andrew J. Parker, M.D. Journ. Acad. Nat. 
Sci. Philadelphia, 2nd series, vol. x , 1896, pp. 247 to 362 ; with fifteen plates 
and several figures in the text. 
NO. 1435, VOL. 55] 
fissures” are produced by mechanical causes, whilst others owe 
their origin to morphological processes of growth in the brain 
substance ; the fissures, of course, representing lines of retarded 
growth. During early development, it is the brain which modi- 
fies the shape and structure of the skull, rather than the reverse ; 
ultimately, as the skull grows more rigid, its influence is shown 
in the increasing tortuosities of the folds. 
The development of the human brain is traced out, so far as is 
necessary to explain the author's views, and the various stages are 
compared with the adult brain of monkeys. At the age of three 
months the fcetal human brain consists of three lobes, which he 
terms the “‘ occipito-frontal,” ‘‘ occipito-temporal,” and ‘‘ occi- 
pital.” It does not immediately appear evident why the author 
employs compound names for the two former lobes, unless it be 
to insist as strongly as possible upon the fact that there is no 
such thing as “* parietal lobe,” at any rate as a morphological 
equivalent of the others. The ‘‘island of Reil” is not homo- 
logous with a ‘‘ lobe,” but is developed at the bottom of a de- 
pressed area, the fossa sy/vz7. Each of the three lobes contains 
a portion of the lateral ventricle ; each will exhibit a similar, and 
symmetrical series of furrows. He points out here, as else- 
where, that the ‘‘ occipital” lobe, developed as it is round the 
posterior cornu of the lateral ventricle, is peculiar to the Primates. 
During the third month a certain number of ‘temporary 
furrows” make their appearance on the surface of the hemi- 
spheres ; they radiate from the region of the sylvian fossa, and 
when viewed from the mesial surface, lines drawn through all 
but those in the occipital lobe meet at a centre which lies in the 
cerebral peduncle: and the angle included between any two 
neighbouring lines is constantly 60°, or thereabouts. This fact 
he makes use of in considering the causes concerned with the 
production of these fissures, which he attributes to pressure 
between brain and skull. 
But, as is well known, these temporary fissures disappear, and 
the brain again becomes smooth for a short time at about the 
fifth month ; and he lays great stress on this smooth brain, with 
its three lobes, a sylvian fissure, a calcarine fissure, and ‘‘ mesial 
arched fissure.” The author regards this stage as the funda- 
mental plan of the Primate brain ; indeed, this is essentially the 
marmoset’s brain enlarged, Later on, new fissures appear, and 
he recognises, in addition to the (1) fundamental er primary fis- 
sures, just mentioned, the (2) secondary fissures, (3) sulci of 
Pansch, mere vegetative repetitions of (2); (4) sulculi, which 
are inconstant, and (5) rami, which are the branches of (2) or 
(3). The mesial arched fissure gives rise to the callosal and 
the hippocampal fissures ; each of which, with the calcarine, is 
similarly related to one of the three primary lobes. 
The occipital lobe next becomes definitely marked off from 
the rest by two fissures, a dorsal and a ventral, constituting 
the ‘‘ primary occipital arch.’ The dorsal one is the ‘‘ parieto- 
occipital” or ‘* perpendicular fissure” of monkeys. The 
mesial ends of these are symmetrical with regard to the cal- 
carine. ‘These fissures, again, are regarded as being due to 
pressure. pias as + af 
This stage represents the characteristic Simian brain (in- 
cluding that of man). ; 
Parker disagrees with the usual view, that the /issze of 
Rolando is a primary fissure; nevertheless, it is certainly 
characteristic of the primate brain, for it occurs in no other 
order. He explains the fissure in an ingenious manner, by 
reference toa lemur’s brain, in which there are two longitudinal 
fissures extending along the fronto-occipital lobe ; a part of the 
upper one is supposed to become vertical. But no ontogenetic 
evidence is forthcoming for this view, which would lead us back 
readily to the condition of a carnivore’s brain. ; 
It is impossible to give briefly his many interesting sugges- 
tions as to the homologues of the frontal and parietal con- 
volutions ; but special interest will be taken in his account of 
the occipital convolutions, for these have always troubled 
anatomists, who have until recently regarded them as being 
more or less irregularly arranged, and consequently have 
neglected them. Parker endeavours to show that they can be 
reduced to order, especially if the development of the ‘‘ plis de 
passage” or ‘‘annectant gyri” be taken into account. These 
rise up, as I have shown in discussing the brain of the chim- 
panzee ‘*Sally,” and as others have also shown, from the 
bottom of fissures; so that in one brain they may be hidden, in 
another they come to the surface and divide single fissures into 
two. Parker says: ‘‘ The typical fissures represent the lines of 
least resistance to the differential action of the pressure forces. 
