722 J. Marion Read 



shows that these mothers lost weight rapidly during this period. 

 Table VI gives the percentage of weight gained or lost every second 

 day by five mothers who gave birth to premature, dead litters. 

 Fig. 2 shows the curve constructed from this data. A distinct 

 loss of weight is shown after 50 days. Whether or not this pheno- 

 menon has any connection with growth cycles, it is impossible now 

 to say with certainty. But it is possible that the death of the young 

 in utero may be due to a failure of the second cycle to connect 

 properly with the first. The fact of the death in utero at this period 

 is undeniable and I mention it as possibly having some significance 

 and bearing upon this and perhaps other questions of intra-uterme 

 development. 



In conclusion, I may say that I realize fully the fact that the 

 data upon which the curve has been constructed have been obtained 

 indirectly and that more accurate data could be obtained only by 

 the sacrifice of hundreds of animals. But as a first attempt to arrive 

 at the truth in regard to the appearance of a curve representing the 

 growth following fertilization, I it submit with the hope that it may 

 serve as a starting point for further work. 



Summary and Conclusions. 



From the facts and figures set forth and discussed in this paper 

 and from the appearance of the curve constructed from the data, it 

 seems reasonable to conclude that: 



I. It is possible to obtain a curve showing the growth of em- 

 bryos in utero by indirect means, i. e. by weighing the mother at 

 regular intervals during pregnancy. 



II. In the case of guinea-pigs, one cycle begins at fertilization 

 of the ova and ends about 60 days after. Another cycle begins a 

 little before the end of the first cycle and continues on after birth. 



III. In both the guinea-pig and man birth occurs during the 

 course of a cycle and not at or near the juncture of two cycles. 



IV. The human young are born before the completion of the 

 first cycle, while the guinea-pig completes one cycle and begins 

 a second in utero. It is quite likely that this fact accounts for the 

 advanced state of development of the latter animal at birth. 



