EXPLANATION OK PLATE 28. xli 



Plate 28. 



Series D. Sections chosen at intervals from a complete series traversing the 

 peritoneal opening of the MUUerian duct, the remnant of the head-kidney, and the 

 termination of the Miillerian duct. Zeiss C, ocul. 3 (reduced one-third). 



Nos. I and 2. Sections through the persistent anterior opening of the head- 

 kidney (abdominal opening of Miillerian duct). The approach of the Wolffian duct 

 to the groove may be seen by a comparison of these two figures. In the sections in 

 front of these (not figured) the two are much more widely separated than in No. i. 



No. 3. Section through the Miillerian duct, just posterior to the persistent 

 opening. 



Nos. 4 and 5. Remains of the ridges, which at an earlier stage connected the 

 first and second grooves, are seen passing from the Miillerian duct to the peritoneal 

 epithelium. 



No. 6. Rudiment of the second groove {^'o.) of the he.-id-kidney. 



Between 6 and 7 is a considerable interval. 



No. 7. All traces of this groove (^j-) have vanished, and the Miillerian duct is 

 quite disconnected from the epithelium. 



No. 8. Rudiment of the third groove {gr.^-). 



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. II. 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. 2. A comparison 

 of the two figures shews 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 embrj'o in which the head-kidney was only represented by a rudiment. (The 

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

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



No. 1. 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 MUUerian duct has vanished. 



Series i. Sections through the hinder end of the MUUerian 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 MUUerian duct is dilated, 

 and its cells are vacuolated. 



