KXI'LANATION OF PLATE 2/. 



gc. Germinal epithelium, mrb. Malpighian body, me. Mesentery, md. MUllerian 

 duct. r r First ridge of head-kidney, r^. Second ridge of head-kidney. r y Third 

 ridge of head-kidney. IV d. Wolffian duct. x. Fold in germinal epithelium. 



PLATE 27. 



SERIES A. Sections through the head-kidney at our second stage. Zeiss 2, ocul. 

 3 (reduced one-third). The second and third grooves are represented with the ridge 

 connecting them, and the rod of cells running backwards for a short distance. 



No. r. Section through the second groove. 



No. 2. Section through the ridge connecting the second and third grooves. 



No. 3. Section passing through the same ridge at a point nearer the third groove. 



4, 5, 6. Sections through the third groove. 



Xo. 7. Section through the point where the third groove passes into the solid 

 rod of cells. 



No. 8. Section through the rod when quite separated from the germinal epi- 

 thelium. 



No. 9. Section very near the termination of the rod. 



No. 10. Last section in which any trace of the rod is seen. 



SERIES B. Sections passing through the head-kidney at our third stage. Zeiss C, 

 ocul. 2. Our figures are representations of the following sections of the series, section 

 i being the first which passes through the anterior groove of the head-kidney. 



The Miillerian duct extends through eleven more sections. 

 The first groove (gr^) extends to No. 3. 

 The second groove (gr z .) extends from No. 4 to No. 7. 

 The third groove (gr y ) extends from No. n to No. 13. 

 The.- first ridge (r r ) extends from No. 2 to No. 5. 

 The second ridge (r z .) extends from No. 8 to No. 1 1. 



The third ridge (r y ) extends from No. 13 backwards through twelve sections, 

 when it terminates by a pointed extremity. 



C. Section through the ridge connecting the second and third grooves of 

 cidney of an embryo slightly younger than that from which Series B was 

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



The fold of the germinal epithelium, which gives rise to a deep groove (x) 

 '.xl to the head-kidney is well marked. 



Section, through the rod of cells constituting the termination of the 

 -t at a stage in which the head-kidney is still present. Zeiss C, ocul. 2. 



