154 NATURAL SCIENCE [September 
Japan, we have a fresh instance of the admirable work done 
by certain ‘of the Japanese morphologists. Mitsukuri’s researches 
concern the fate of the blastopore, the relations of the primitive 
streak, and the formation of the posterior end of the embryo in 
Chelonia, together with some remarks on the nature of meroblastic 
ova in vertebrates. But, as is not infrequently the case, the most 
important results are those which receive least consideration in the 
title of the paper.. The nature and fate of the ‘ yolk-plug’ (or cell- 
mass projecting between the lips of the blastopore), which undergoes 
very complex changes and shiftings of position, is far more interest- 
ing than that of the blastopore itself, owing to the theoretical con- 
siderations which Mitsukuri’s view of it involves. The previously- 
asserted homology of this cell-mass with the yolk-plug of the 
Amphibia, and with a similar structure observed by Van Beneden in 
Mammalia, is well-maintained. The necessity for a re-classification 
of vertebrate ova into ‘primary’ and ‘secondary’ types is clearly 
established, if the theory of the loss and acquisition of yolk in verte- 
brate eggs several times in the course of phyletic development be 
correct. The primitive plate and yolk-plug in Chelonia are shown 
to be rudiments of a large primary yolk-mass which existed in the 
early history of amniote eggs. The large yolk-mass seen in amniote 
eggs of the present day has been secondarily acquired, and the 
enclosure of this mass by the blastoderm is a coenogenetic process 
having nothing to do with gastrulation. On the other hand, the 
enclosure of the primary yolk-mass by the blastoderm is closely 
connected with gastrulation. Mammalian ova are supposed to have 
lost even the secondary yolk-mass. Any comparison, therefore, 
between the various classes of ova can only justly be made when 
these facts are given due weight, and they are likely to throw 
additional light on questions dealing with the primitive character or 
otherwise of various groups. 
PRIMITIVE METHODS OF TREPANNING 
In Anthropologie (vol. viii., pt. i., 1897) a most interesting account 
is given by Dr H. Malbot, assisted by Dr R. Verneau, on the Tre- 
panning of the Skull by the Chaouias of the Aurés Mountains, in the 
province of Constantine, Algeria. A preliminary account of these 
people and their country was given in the previous number of the 
same journal. It is a most curious fact that in a remote district in 
the above-named region, this people of mixed racial origin practise 
trepanning on an elaborate scale, and apparently maintain this prac- 
tice as an heritage from ancient times. Trepanned skulls have been 
found in ancient cemeteries in Algeria, and prove the practice to be 
an old one in the region. The Chaouias have established a great 
