MODIFICATION OF THE GERM-CELLS IN MAMMALS 159 



periods after the embryos are of sufficient size to be detected by 

 this method of external examination. To convey some idea of 

 how accurately one may detect a structure by palpation through 

 the abdominal wall of the guinea-pig, it may be stated that a 

 slightly cystic ovary has frequently been diagnosed by such an 

 examination. 



A normally developed embryo 19 mm. crown rump length is 

 shown in figure 6 and near it is seen an amorphous embryonic 

 mass 2 mm. in longest diameter which represents the other 

 member of the litter. The two were in different horns of the 

 uterus. The placenta of the normal embryo was of the usual 

 size, while the one associated with the arrested specimen was 

 only about one-half as large. The entire mass of the smaller 

 ovum in the uterus was about that of a ten-day specimen, while 

 the normal individual was a typical twenty-day specimen. This 

 case was detected by external examination and was merely opened 

 in order to use the embryos for illustrating the phenomenon. 

 In the explanation of the figure the ancestry of the embryos is 

 given. 



The intrauterine absorption of embryos, as stated above and 

 indicated in table 1, may occur in normal guinea-pigs. A. W. 

 Meyer ('17) has very recently described the histological con- 

 ditions found in partially absorbed embryos which he had ob- 

 tained during a study of the prenatal growth of the guinea-pig. 

 There is considerable data from our study, to indicate that this 

 absorption of embryos is somewhat more frequent in the alcoholic 

 than in the normal lines. 



7. A COMPARISON OF THE QUALITIES IN THE DIFFERENT GEN- 

 ERATIONS OF THE ALCOHOLIC LINES AS THEY BECOME 

 FURTHER REMOVED FROM THE GENERATION 

 DIRECTLY TREATED 



It has been mentioned in discussing the improvement of the 

 records in table 1, as compared with our previous reports, that 

 this advantage is partly due to the larger number of late-gen- 

 eration animals at present included. We may now analyze the 

 alcoholic lines for a comparison of the qualities of the early and 



