THE DEVELOPMENT OF THE EMBRYO 1143 



whereas fat stained with Sudan-red actually reaches the intervillous 

 spaces, it reappears as unstained globules within the syncytium of the 

 villi. But even the pigment so separated traverses these cells and 

 circulates in the fetal blood-. Glycogen is found in all the tissues of 

 the embryo during its period of most active growth, although later on, 

 when the liver becomes functional, it disappears almost completely 

 from the skin, lungs and other organs. In order to effect these reduc- 

 tions and syntheses, the chorionic epithelium must be in possession of 

 different enzj^mes, an assumption which has more recently found 

 experimental proof in the work of Bergell and Folk,^ and others. 

 Thus, the especially high requirement of the fetus in salts may bring it 

 about that the bones, and particularly the teeth, of the mother become 

 affected. Some women are more prone to suffer from this partial 

 decalcification than others, a difference which seems to be associated 

 with their varying power of assimilating calcium from their food. 



It is also a well-known fact that drugs may be transmitted from 

 the mother to the fetus, as well as in the reverse direction. This is 

 true of potassium cyanid, alcohol, strychnin, and many inorganic 

 and organic salts. Bacteria as such are rarely transferred, so that 

 the placenta may be regarded as playing the part of a filter. This 

 power it loses if diseased. Neither does it seem to be able at any time 

 to exclude toxins. ^ 



Determination of Sex.: — In 1897 Schenk made the startling claim 

 that the nutrition of the embryo may be influenced in such a way as 

 to produce either a male or a female offspring. This speculation he 

 based upon the older view which contends that sex is dependent upon 

 the nutritive superiority of the father or mother. The work of Rauber,^ 

 Morgan,^ Wilson^ and Doncaster,^ however, has proved that sex is 

 determined before the beginning of segmentation, i.e., either at the 

 time or immediately after the union of the sperm-cells. The actual 

 factor here concerned seems to be the spermatozoon which may or 

 may not embrace an accessory chromosome. Thus, it has been found 

 that the spermatocytes of many animals contain an odd number of 

 chromosomes, while in the oocytes they appear in pairs and are ar- 

 ranged in a similar manner. In fact, the spermatocytes are said to 

 appear in three forms, namely : (a) one in which a centrosome remains 

 without a mate, (h) one in which the chromosomes of one pair differ 

 in size, and (c) one in which they are all alike. The reduction, in the 

 number of these chromosomes during fertilization must then give rise 

 to three types of spermatozoa, namely : (a) one in which an odd chro- 

 mosome is present, (6) one in which the number of the chromosomes 

 is even but in which a small or aberrant chromosome is present, and 



1 Miinchener med. Wochenschr., 1908. 



^Lubarsch, Ergebn. der allg. Path, und path. Anat., 1896. 



^ tJberschuss an Knabengeburten und seine biol. Bedeutung, Leipzig, 1900. 



^ Heredity und Sex, New York, 1913. 



^ Jour, of Exp. Zoology, iii, 1906, and Science, 1909. 



^ The Determination of Sex, Cambridge, 1914. 



