262 



SCIENCE 



[N. S. Vol. LIII. No. 1368 



tiie blood cells die appearance of multiple 

 drops into which the granuloplasm moves sub- 

 sequently as it does into typical pseudopods. 

 Transition can be observed between these 

 drops and the typical pseudopods. 



It is also possible to produce experimentally 

 in the amoebocytes structures which very 

 closely resemble ova in which maturation 

 membranes have formed. Jacques Loeb has 

 formerly shown that this formation depends 

 upon a proces of cytolysis. In the blood cells 

 these structures appear under conditions in 

 which the cell has taken up fluid from the 

 surrounding medium and the consistency of 

 the protoplasm resembles that of a liquid. 

 All kinds of transition between these struc- 

 tures, drop pseudopods and the typical tongue- 

 like pseudopods can be found. These and 

 other observations very strongly suggest that 

 the formation of pseudopodia, the appearance 

 of drops at the surface of the cells and the 

 formation of fertilization membranes are 

 related phenomena and that the latter two 

 conditions represent extremes ia a process 

 which, when acting in medium intensity, leads 

 to the formation of the typical pseudopodia. 



4. Through changes iu the consistency of 

 the protoplasm in the blood cells of Limulus 

 it is possible to imitate the structures corre- 

 sponding to different tissues. Especially did 

 we obtain in certain cases through an increase 

 in the consistency of the cells tissues which 

 resembled those composed of ganglia and glia 

 cells. It may thus be possible to obtain indi- 

 cations as to some of the conditions which 

 induce the cells of different tissues to assume 

 different forms. 



Leo Loeb 



Washington Univeesitt 



the relative numbers of twins and 

 triplets! 



It miay be of interest to call attention to a 

 simple relation between the nvmiber of human 

 twin and triplet births. The relation was 

 noticed a number of years ago and I supposed 



1 Contribution, from the Zoological Laboratory of 

 the University of Illinois, No. 172. 



it had been recorded, but a search has failed 

 to reveal any published statement. 



If 1/n is the proportion of twin births to 

 all births ia a large population during any 

 period, then the proportion of triplet births 

 during the same period is very near to 1/n-. 

 The agreement of the data is often startling. 

 Thus in 13,360,557 births in Prussia during 

 the years 1826-1849 as recorded by Veit^ the 

 number of twin births is one in 89.1 and the 

 number of triplet births one in (88.9)^. In 

 1,339,975 births in the United States registra- 

 tion area in 1917' the number of twin births 

 is one in 93.1 and the number of triplet births 

 one iu (93.0)=. 



From the statistical relations it would ap- 

 pear that triplets are produced by the coin- 

 cidence of two independent processes occur- 

 ring with equal frequencies. One of these 

 processes by itself gives rise to twins. This 

 relation would apply to any mode of origin of 

 multiple births or to different combinations 

 of them provided that each followed the rule. 



The principle might be applied to the two 

 chief explanations of multiple births as 

 follows : 



1. Multiple Ovulation. — Normally a single 

 ovum is discharged from the ovaries. There 

 is some coordinating mechanism which pre- 

 vents the ripening of other ova at the same 

 time. Suppose that as a result of a purely 

 intrinsic factor, once in n times an ovum 

 appears which fails to respond to this mech- 

 anism. The chance that two such extra ova 

 will appear at the same time is once in n 

 squared. Obviously this presupposes that the 

 failure to respond is due to independent 

 processes in the two ova. To put the case 

 more concretely, suppose that the approach to 

 maturation of an ovum is accompanied by an 

 internal secretion which acts upon other ova 

 and keeps them from completing the process 

 at the same time. The overwhelming major- 



2 Veit, G., 1855, Monatsschrift fur Geburtskunde 

 und FrauenJcran'kheUen, 6: 127. 



3 Birth statistics for the birth registration area 

 of the United States, 1917, U. S. Bureau of the 

 Census, Washington, 1919. 



