DESCRIPTION OF PLATES 27 AND 28. 643 



No. 8. Rudiment of the third groove (gr a .). 



No. 9. Miillerian duct quite free in the space between the peritoneal epithelium 

 and the Wolffian duct, in which condition it extends until near its termination. 



Between Nos. 9 and 10 is an interval of eight sections. 



No. 10. The penultimate section, in which the Miillerian duct is seen. A lumen 

 cannot be clearly made out. 



No. n. The last section in which any trace of the Miillerian duct is visible. No 

 line of demarcation can be seen separating the solid end of the Miillerian duct from 

 the ventral wall of the Wolffian duct. 



FIGS. E. and F. Sections through the glomerulus of the head-kidney from an 

 embryo prior to the appearance of the head-kidney. Zeiss B, ocul. i. A comparison 

 of the two figures shows the variation in the thickness of the stalk of the glomerulus. 

 E. Section anterior to the foremost Malpighian body. F. Section through both the 

 glomerulus of the head-kidney and that of a Malpighian body. The two are seen to 

 be connected. 



SERIES H. Consecutive sections through the hind end of the Miillerian duct, 

 from an embryo in which the head-kidney was only represented by a rudiment. (The 

 embryo was, perhaps, very slightly older than that from which Series D was taken.) 

 Zeiss C, ocul. 3 (reduced one-third). 



No. i. Miillerian duct is without a lumen, and quite distinct from the Wolffian 

 wall. 



No. 2. The solid end of the Miillerian duct is no longer distinct from the internal 

 wall of the Wolffian duct. 



No. 3. All trace of the Miillerian duct has vanished. 



SERIES i. Sections through the hinder end of the Miillerian duct from an embryo 

 of about the middle of the sixth day. Zeiss C, ocul. 2 (reduced one-third). 



No. i. The Miillerian duct is distinct and small. 



No. 2. Is posterior by twelve sections to No. i. The Miillerian duct is dilated, 

 and its cells are vacuolated. 



No. 3. Penultimate section, in which the Miillerian duct is visible ; it is separated 

 by three sections from No. 2. 



No. 4. Last section in which any trace of the Miillerian duct is visible ; the 

 lumen, which was visible in the previous section, is now absent. 



No. 5. No trace of Miillerian duct. Nos. 3, 4, and 5 are consecutive sections. 



FIG. K. Section through the hind end of the abdominal opening of the Miillerian 

 duct of a chick of 123 hours. Zeiss C, ocul. i (reduced one-third). It illustrates the 

 peculiar cord connecting the Miillerian and Wolffian ducts. 



