286 SUMMARY OF CURRENT RESEARCHES RELATING TO 



umbilical region, leaving the skeletal structures of both sternum and 

 pelvis entirely unconnected with one another. The union was exactly 

 face to face, except for the fact that the umbilical cord is single and 

 comes off from one side of the central mass. The omphalopagous type 

 of monstrosity finds its best illustration among the osseous fishes. In 

 trout and salmon, for instance, union of symmetrical twins by the 

 yolk-sac only is by no means uncommon, as Gemmill has shown. In 

 rare cases survival for a time may occur. As Geoffrey Saint-Hilaire 

 pointed out, omphalopagous union can readily occur wherever the egg 

 is large and the yolk-sac is not cast off but taken into the body. In 

 reference to the human case described, the twins are uni-oval in origin. 

 The germinal areas from which they developed were probably situated 

 opposite one another on the wall of the blastocyst. There may have 

 been only one endodermic sac, but more probal;)ly there were two such 

 sacs which became confluent posteriorly on their ventral aspects. 



Prolonged Gestation in Suckling Mice.* — W. B. Kirkman has 

 inquired into the lengthening out of the gestation period, when the 

 females suckle their young during pregnancy. He has brought together 

 data from which it is possible to determine, within the possible error of 

 one day, the age of all embryos obtained from non-suckling white mice. 

 Ovulation, fertilization, and the early cleavage of the eggs bear the 

 same time relations to parturition and to one another in both suckling 

 and non-suckling white mice, except that the former are much more apt 

 to skip an ovulation period. 



Implantation of embryos in the uterus occurs in non-suckling white 

 mice on the fifth day following parturition (provided the female did not 

 skip an ovulation cycle). Implantation of embryos in the uterus occurs 

 in suckling white mice, with three or more young, on the fourteenth 

 day following parturition (provided the female did not skip an ovulation 

 cycle). In these lactating females the blastulai lie free in the lumen of 

 the uterus from the sixth to the fourteenth day post-partum. This is 

 supposed to be due to the activity of the mammary glands. 



The available material of stages following implantation in suckling 

 females shows no evident correlation with either the number of nursing 

 young or the number of embryos being carried. It is also impossible at 

 present to reconcile the development of these embryos with the observed 

 facts regarding the time of parturition in suckling mice. 



Effect of Extirpating Hypophysis on Growth and Development 

 of Frog-t — P. E. Smith finds that the removal of the hypophysis makes 

 the growth of tadpoles slower than the normal. The hypophysectomized 

 specimens were perhaps more alert than the checks ; they were more 

 resistant to a disease which attacked both them and the others. They 

 Were much lighter in colour, there being fewer melanophores and fewer 

 melanin granules in them. The growth of the hind legs was greatly 

 inhibited ; in most cases there was no growth of the buds of the hind 



* Anat. Record, xi. (1916) pp. 31-40, 



t Anat. Record, xi. (1916) pp. 57-64 (10 figs.). 



