Figure 15_e_ is through the middle region of the embryo, and, owing to the curvature of the body, is not an exact dorso-ventral section; this accounts, in part at least, for the unusual diameter in a dorso-ventral direction of the aorta (_ao_), which is very large in proportion to the other structures. The posterior cardinal vein is shown on the left, but not on the right. The relative sizes of the spinal cord (_sc_) and notochord (_nt_) are very different from what was seen in the preceding figure. In this section the spinal cord is considerably smaller than in the preceding, while the notochord is very much larger; in fact the notochord here seems abnormally large when compared to corresponding sections of other series. It is true, however, that while the spinal cord has been diminishing in diameter the notochord has been increasing. The spinal cord, notochord, and dorsal aorta are all so large that they are flattened against each other, the pushing in of the ventral side of the spinal cord being even more marked than is shown in the figure. On either side of the spinal cord a large spinal ganglion (_sg_) is seen, closely wedged in between the spinal cord and the adjacent muscle plate (_mp_). As in the preceding stage, there is a marked space between the muscle plate and the adjacent ectoderm (_ec_). The somatic mesoblast at the upper angle of the unenclosed body cavity is thickened on each side and somewhat bulged out by the Wolffian body to form what might be termed a Wolffian ridge (_wr_). In the mid-ventral line is the considerably developed mesentery (_ms_), from which the intestine has been torn. The Wolffian bodies now consist, on each side, of a group of five or six tubules (_wt_) of various sizes, near which in a more ventro-lateral position, close to the upper angle of the body cavity, is the more distinct Wolffian duct (_wd_). The allantois is fairly large by this time, and may be seen in the most posterior sections as an irregular, thick-walled outgrowth from the hindgut.