590 MALCOLM LAURIE. 



The embyro uudergoes the whole of its development in the 

 diverticulum, and does not pass into the ovarian tube until it is 

 ready to be born. 



The development extends over more than six months, my 

 earliest stages having been preserved towards the end of 

 October and the latest in May. How much longer it may take 

 I cannot say, but the oldest embryos which I have examined 

 are still some way from being fully developed. 



Development of the Embryo. 



In the earliest stage examined by me the ovum is com- 

 pletely segmented. The external appearance of the diver- 

 ticulum and appendix is shown in fig. 1, and has been 

 described above. A transverse section (fig. 6) shows the 

 ovum, which is about '12 mm. in diameter, to consist of an 

 irregular mass of cells with faintly marked outlines and large 

 oval nuclei. There appear to be spaces between the cells, but 

 this may very likely be due to shrinkage. The nuclei for the 

 most part stain very faintly with carmine, and show a slightly 

 granular structure. Here and there one of the nuclei stains 

 very darkly, and such nuclei appear to be undergoing divi- 

 sion. The nuclei are scattered about irregularly, and show no 

 tendency to the formation of layers. There is no trace of 

 yolk either in the cells or in the spaces between them. 



In the next stage, between which and the one described 

 above there is a considerable gap, various changes have taken 

 place. The ovum has increased in size to about '15 mm. 

 diameter, though there is considerable individual variation in 

 this respect, and shows the beginnings of several structures. 

 The cells are chiefly aggregated along one side — the ventral — 

 and towards the posterior end, leaving a space in the middle 

 which is full of finely granular substance. This space is well 

 seen in longitudinal section (fig. 8), and a section in this 

 direction also shows very clearly the stomodaeum (figs. 7 

 and 8, st.). This structure is a tube, the walls of which are 

 at first one cell thick (fig. 7, st.), and the lumen of which 

 opens to the exterior of the embryo at the anterior end (i. e. 



