178 SUMMARY OF CURRENT RESEARCHES RELATING TO 



certain cells of the blastocyst endoderm (yolk-sac endoderm) daring 

 secondary bud formation. The path of the migration is from the 

 embryonic endoderm into the intestinal wall, thence into the surrounding 

 mesenchyme to the mesentery, and onward into the germinal epithelium. 

 No germ-cells are found at any stage in the blood-vessels. It may be 

 concluded that the germ-cells of the four embryos of one vesicle do not 

 have a common origin, in the sense of having arisen from a pre-localized 

 region of the early plastocyst. 



Maturation of Ovum in Swine.* — George W. Corner has studied 

 the maturation phenomena in swine. This is the first case in which the 

 maturation of the ova of an Ungulate has been observed. The sequence 

 is the same as in previously-studied forms of other orders, the first 

 polar body being extruded, and the second polar division proceeding as 

 far as spindle formation before fertilization occurs, the second polar 

 body being cut off only after the entrance of the spermatozoon. 



Polyembryonic Blastocyst in Opossum.! — J- J- Patterson and 

 C. G. Hartman describe a blastocyst of Didelphys virginiana which con- 

 tained four embryos, three abnormal and one normal. The arrangement 

 of these on the blastoderm suggests a certain similarity to the condition 

 in the armadillo (Tatusia novemcincta), where four are normal. It is 

 possible that the rare occurrence of multiple-embryo formation in 

 B. virginiana has become a permanent phenomenon in the development 

 of D. marsupiaUs, as reported by Bluntschli. In any case we have here 

 the rare case of a polyembryonic blastocyst in a multiparous mammal. 



Superfetation in Cat.J — Mary T. Harman notes that the word 

 " superfetation " has been used to denote that condition in which the- 

 uterus contains embryos of different degrees of development. This 

 condition may result from a second coition, or a second conception may 

 have taken place without a second coition. Although superfetation is- 

 rare and abnormal, many cases have been reported in man and in other 

 mammals which do not seem to be satisfactorily explained, except on the 

 supposition that a second conception has taken place. It is possible 

 that all cases of superfetation are not attributable to the same cause. 

 In the case of the cat described in this paper it seems as reasonable to 

 think of the less advanced embryo of the four as the result of delayed 

 fertilization, as to account for it on the ground of delayed development. 

 or a second coition. 



Effect of Vital Stains on Eggs.§— Margaret Eeed Lewis finds that 

 the eggs of the Nemertean Cerehratidus lacteus may take up Janus green 

 in their gelatinous membrane, and may thereafter develop up to the 

 fourth or eighth cell-stage before they are killed by the stain. The- 

 membrane keeps the stain back. Unprotected eggs are at once killed by 



* Anat. Record, xiii. (1917) pp. 109-12. 



t Anat. Record, xiii. (1917) pp. 87-95 (2 pis. and 1 fig.). 



t Anat. Record, xiii. (1917) pp. 145-57 (2 pis.). 



§ Anat. Record, xiii. (1917) pp. 21-35. 



