430 



Mr. A. Eraser. On the Inversion of the [Dec. 21,. 



VI. " On the Inversion of the Blastodermic Layers in the Rat 

 and Mouse." By Alexander Fraser, M.B., &c, the Owens 

 College, Manchester. Communicated by Allen Thomson, 

 F.R.S. Received December 18, 1882. 



Having been engaged since May, 1881, in the investigation of the 

 early placentation in some of the Rodentia, rat, mouse, and guinea- 

 pig, in which it presents peculiar features, I was so fortunate in the 

 commencement of July of the present year to ascertain the fact that 

 in the common grey rat and its white variety, an arrangement of the 

 blastodermic layers existed, similar to that which had been known in 

 the guinea-pig since the publication of Bischoff's observations in 

 1852. 



I was able, early in August, to extend this fact so as to include the 

 common house mouse and its white variety. 



These facts were ascertained by the examination of entire series of 

 microscopic sectious made in three different planes of the uterine 

 loculi of rats and mice pregnant from the eighth to the tenth day. 

 For the method used in imbedding I am indebted to the kindness of 

 Professor His, Director of the Anatomische Anstalt in Leipzig, 



These facts were communicated to Dr. Thomson early in July, and 

 formed the subject of an oral statement made to the Biological Section 

 of the British Association at the Southampton Meeting in August. 



At that period my observations did not cover a stage early enough 

 to enable me to give a satisfactory explanation of the inversion, but 

 since that date I have been occupied in tracing the history of the ova 

 in the rat, mouse, and guinea-pig from the time of their leaving the 

 ovary up to the thirteenth day of pregnancy. My observations on 

 the ova up to the sixth day are as yet incomplete, but as the inversion 

 can be explained from ova of this date and onwards, I do not hesitate 

 to offer them to the Society. 



From the sixth day onwards to the thirteenth I have made, at in- 

 tervals of four hours, series of sections from pregnant loculi in three 

 different planes as already stated. 



The remarks which are to follow will have reference chiefly to the 

 rat (so far as the ovum is concerned) in which animal my work has 

 been more complete than in the other two, and I shall deal first with 

 the changes taking place in limited areas of the mucous membrane of 

 the uterus, leading to the formation of the decidua, and onwards to 

 the fully formed maternal portion of the placenta, and secondly with a 

 brief outline of the developmental phenomena, so far as these are 

 peculiar, from the sixth day onwards to the thirteenth. 



