1918.J ANIMAL PRODUCTION. 573 



The currents of morphological thought are three — the functional or synthetic, 

 the formal or transcendental, and the materialistic or disintegrative. " Is func- 

 tion the mechanical result of form, or is form merely the manifestation of func- 

 tion or activity?" The author is in sympathy with the functional attitude. 

 Theories of evolution have blinded us to the questions of vital phenomena, and 

 the opinion is hazarded that we will return to a simpler attitude toward the 

 problems of animal form. 



Embryolog-y of the yellow mouse, W. B. Kiekham (Ahs. in Anat. Rec, 11 

 (1917), No. 6, pp. Jf80, Ji81). — Material from nonsuckling yellow mice represent- 

 ing embryonic stages of each of the first 19 days of pregnancy was compared 

 microscopically with similar material from nonsuckling white mice. 



It was found that the rate of cleavage and of embryonic development is the 

 same for yellow as for white mice. All of the observed two-cell stages of both 

 yellow and white mice appear normal. No degenerating morulse or blastulse 

 were found in white mice, while one or more were present in every yellow mouse 

 containing embryos of that stage in development. The material covering the 

 sixth to the seventeenth days of pregnancy yielded degenerating embryos in 8 

 out of 28 uteri in white mice and in 11 out of 13 yellow mice. If females 

 that have stillbirths or that eat their new-born young are eliminated, the figures 

 become more striking, degenerating embryos in white mice appearing in only 1 

 uterus out of 12 examined, while in yellow mice 11 out of 12 uteri contained 

 them. No degenerating embryos were found in either white or yellow mice 

 pregnant more than 16 days. [Apparently the author did not test genetically 

 the white mice. It is possible that some of them carried the factor for yellow 

 color.] 



Evidence for the death in utero of the homozygous yellow mouse, H. L. 

 Ibsen and E. Steigleder {A^ner. Nat., 51 {1911), No. 612, pp. 740-152, fig. 1).— 

 Data are presented substantiating the conclusions of Castle and Little (E. S. 

 R., 24, p. 475) and Kirkham (see above) that in mice homozygous yellow zygotes 

 are produced in the yellow X yellow mating, but that these zygotes fail to develop 

 normally after implantation in the uterus. In the studies here reported 688 

 embryos were obtained from nonsuckling females pregnant from 13 to 19 days. 

 These embryos were from the following matings: (1) Yellow? X yellow $, 

 (2) yellow $ Xnonyellow (chocolate) $, (3) nonyellow (chocolate) $ X yellow 

 $, and (4) nonyellow $ Xnonyellow $. In this last mating most of the 

 parents were self-blacks. 



During the investigation two types of dead embryos were encountered, (1) 

 those in which development had ceased shortly after implantation, and (2) a 

 few which had died after apparently normal development of about 13 days. 

 The average number of living embryos was less for the mating yellow X 

 yellow than for any of the other types of matings, singly or combined. In 

 the yellow X yellow matings the average of 33 litters was only 6.15, while for 

 49 litters of the other matings combined the average was 7.63. The average 

 litter size when dead embryos are also included was 8.27 for yellow X yel- 

 low and 8.47 for all other matings. Of living litters of mice born in the 

 laboratory during the course of this investigation 140 litters from yellow X 

 yellow averaged 5.36 each and 180 litters from nonyellow Xnonyellow matings 

 averaged 6.56 each. 



In explanation of this failure of homozygous yellow zygotes to develop, it is 

 suggested that in mice there may be a " lethal factor," similar to those so 

 well known in Drosophila, which is so closely linked to the factor for yellow 

 that they are practically at the same locus and there is consequently no crossing 

 over. 



