142 TSABI-ll.LA M. DRTTMMONO, 



op. Operoiiliim. ot. Otooyst. pn. Pei ioardium : r. p. c. Orifjinal rif^lit. 

 division ; /. p. c. Oiij^inal left, division, p. g. Pedal ganglion, p. n. Pedal 

 nerves, r. ap. Renal opening into the mantle cavity, rec. llectum. r.f). ap. 

 Reno-gonadial aperture, r.pc.ap. Reno-pericardial aperture of the original 

 left kidney, r.s, Radula sac. s.g. Sliell gland, s^. Stomacli. mh.c.'&\\}n- 

 oesopiiageal connective, sup. c. Snpra-cesopliageal connective, t. Tentacle. 

 V. Velum, ves. and ves' . Vesicles attached to kidneys, v. h. Visceral hump. 

 a\ Ridge between the two original horns of the mantle cavity on which the 

 anus oprns. 



PLATE 7. 



Fig. 1. — Slightly oljlirpie transverse section througli the visceral hnni]) of 

 an cndjryo between the age of that shown in Fig. C and that in Fig. D. 

 Both kidneys and the first rudiment of the heart are shown. X 330. 



Fig. 2. — Oblique section through the extreme (original) left portion of the 

 pericardium of an embryo rather older than that shown in Fig. G. The 

 sharp curve of the surface of the body shown at ect. indicates that the 

 visceral hum]) is just beginning to coil, X 330. 



Fig. 3. — Another section of the same series, and showing the same region, 

 but rather more posterior. Two sections intervene between Figs. 2 and 3. 

 X 330. 



Fig. 4. — The next section posterior to Fig. 3, and showing the same region. 

 X 330. The figure should be rotated about 9 degrees to the left to compare 

 with Fig. 3. 



Fig. 5. — A transverse section through the same region as the above, but of 

 an older embryo in which about one complete turn of the spiral coil of the 

 visceral hump is comitlete. It is one of the same series as Fig. 17. X 330. 



Fig. 0. — An ideal longitudinal section of the whole genital apparatus of an 

 advanced embryo, with about two turns of the spiral complete, reconstructed 

 from a series of tiansverse sections. The gonad is rejiresented spread out 

 instead of coiled. X 140. 



Fig. 7. — A transverse section across the region aa. of Fig. 0. x 330. 



Fig. 8. — A transverse section across the region hh. of Fig. G, showing also 

 tli(! close proximity of the gcniital organs to the liver, x 330. 



Fig. 9. — A transverse section across the region cc. of Fig. 0. x 330. 



Fig. 10. — Sagittal section through an embryo belonging to Stage A. x 

 330. 



Fig. 11. — Transverse section througli the posterior region of t.he visceral 

 hump of an embryo belonging to Stage C, x 119. 



