380 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The occurrence of various duplicities would seem to point to a 

 relatively hiirli prospective potency of parts of the Teleost egg, but it 

 decreases rapidly, for at an early stage (the Randvvulst-stage or there- 

 aljout) these parts are already specifically predetermined as early 

 (undifferentiated) primordia of some organs. If at this stage a fragment 

 be eliminated the result will be a defect of a corresponding organ or 

 patt of the body. Accordingly the teratogenetic time limit must be 

 regarded as very brief, and especially so in the case of duplicities. 



The experiments tend to justify the hypothesis on which they were 

 based, that parental metabolic toxaemia may be the cause, or, at least, 

 the chief cause underlying the origin of monsters. 



Early Development of Spleen in Lepidosiren and Protopterus.* 

 G. L. Purser has studied the early development of the spleen in 

 Lepidosiren and Protopterus. The spleen arises in a thickening of the 

 mesenchyme of the foregut, just after the mesenchyme has become free 

 from yolk-granules. It is, at first, a mass of mesenchyme cells round 

 about which are large venous sinuses without any endothelial walls ; 

 later the cells become arranged to form trabeculse across these sinuses, 

 which thus get broken up into the channels of a sponge-work. The 

 afferent and efferent veins are in very close connexion with the veins 

 from the intestine and to the liver respectively. The arterial supply of 

 blood develops from the coeliac artery rather later. The organ remains 

 throughout ontogeny embedded in the sheath of the foregut, and is 

 therefore inconspicuous. 



Influence of Age on Sex.f — P. J. Ewart discusses the influence of 

 the age of the grandparent at the birth of the parent on the numlier of 

 children born and their sex. The imperfections of the data he has 

 analysed are such that no very decided statements can be made. Still, 

 some credence can be given to the belief that those born during the 

 declining years of life do enjoy an enhanced fertility, which may, 

 however, by the time at which birth occurs, be actually neutralized by 

 the low survival value of their offspring. 



The evidence presented suggests that the pre-natal mortality affects 

 males more than females, that infant and pre-natal mortality are highly 

 correlated, that infant mortality is higher in the case of elderly 

 parturients and also in the case of parturients who are themselves the 

 offspring of elderly parents, and that the differential pre-natal rate 

 increases as age increases. If so, it must follow that the ratio of male 

 to female births should diminish with the age of the parents. But the 

 author's direct investigation of this point leads, if anywhere, to an 

 opposite conclusion. " Hence it must follow that age exerts a direct 

 polarizing influence upon the sexual cell (whether before or after 

 fertilization cannot even be conjectured) sufficient to neutralize the 

 factors which make for the production of an excess of females." 



* Quart. Journ. Micr. Sci., ii. (1917) pp. 231-41 (3 pis.), 

 t Journ. Hygiene, xv. (1915) pp. 127-62 (1 fig.). 



