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. 



Peimitive Methods of Trepanning 



In V Anthropologic (vol. viii., pt. ii., 1897) a most interesting account 

 is given by Dr H. Malbot, assisted by Dr E. Verneau, on the Tre- 

 panning of the Skull by the Chaouias of the Aures 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 Chaou'ias have established a great 



