Early stages of development of the mouse. 61 



A Reinvestigation of the Early Stages of the 

 Development of the Mouse. 



By 



J. W. Jenkiiisoii, M.A., 



Assistant to Uie Linacre Professor of Comparative Anatomy in the Universily 



of Oxford. 



With Plates 5 and 6. 



About a year and a half ago, while working in Professor 

 Weldon's laboratory at University College, London, at cer- 

 tain points in the organogeny of the Mammalia, I cut a series 

 of sections of the pregnant uterus of a mouse, which proved 

 on examination to contain a much younger embi^o than I had 

 anticipated; and on searching through the literature of this 

 subject, I came across, in vol. xxxiii of this Journal, a paper 

 by Eobiuson (26) describing the development of the germinal 

 layers in the mouse and rat, and containing figures which, I 

 found, differed considerably from my own sections. I also 

 found that the observations of the author were not only in 

 startling disagreement with those of earlier investigators — 

 such as Selenka and Duval — on the same genus, but that they 

 were also totally at variance with what might have been 

 expected from the known embryogeny of other types. In 

 addition, the writer of the paper seems to have been so cer- 

 tain of the accuracy of his own description that he ventured 

 to call in question the validity of the interpretations put by 

 others (van Beneden, Hubrecht, Selenka, Duval, etc.) on 

 their own work, and to substitute for them a generalisation 

 founded only on the single form which he had investigated, 

 but which he wished to'apply to the whole of the Mammalia. 

 Still he was able, in a short paper — published subsequently (26) 



