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. 1. 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.
Nos. 4, 5, 6. Sections through the third groove.
No. 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
epithelium.
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 1 being the first which passes through
the anterior groove of the head-kidney.
No. 1 SECTION 3. No. 8 SECTION 13.
" 2 " 4. " 9 " 15.
" 3 " 5. " 10 " 16.
" 4 " 6. " 11 " 17.
" 5 " 8. " 12 " 18.
" 6 " 10. " 13 " 19.
" 7 " 11. " 14 " 20.
The Müllerian duct extends through eleven more sections.
The first groove (_gr_1.) extends to No. 3.
The second groove (_gr_2.) extends from No. 4 to No. 7.
The third groove (_gr_3.) extends from No. 11 to No. 13.
The first ridge (_r_1.) extends from No. 2 to No. 5.
The second ridge (_r_2.) extends from No. 8 to No. 11.
The third ridge (_r_3.) extends from No. 13 backwards through twelve
sections, when it terminates by a pointed extremity.
FIG. C. Section through the ridge connecting the second and third grooves
of the head-kidney 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._) external to the head-kidney is well marked.
SERIES G. Sections through the rod of cells constituting the termination of
the Müllerian duct at a stage in which the head-kidney is still present.
Zeiss C, ocul. 2.