[38] Alexander Agassiz was fortunate enough to succeed in procuring and rearing a batch of eggs of this interesting form. He has given an adequate account of the external characters of the post-embryonic stages, and very liberally placed his preserved material of the stages both before and after hatching at Prof. W. K. Parker's and my disposal. The account of the stages prior to hatching is the result of investigations carried on by Professor Parker's son, Mr W. N. Parker, and myself on the material supplied to us by Agassiz. This material was not very satisfactorily preserved, but I trust that our results are not without some interest. The ova of Lepidosteus are spherical bodies of about 3 mm. in diameter. They are invested by a tough double membrane, composed of (1) an outer layer of somewhat pyriform bodies, radiately arranged, which appear to be the remains of the follicular cells; and (2) of an inner zona radiata, the outer part of which is radiately striated, while the inner part is homogeneous. [FIG. 58. SURFACE VIEW OF THE OVUM OF LEPIDOSTEUS WITH THE MEMBRANES REMOVED ON THE THIRD DAY AFTER IMPREGNATION.] The segmentation, as in the Sturgeon, is complete, but approaches closely the meroblastic type. It commences with a vertical furrow at the animal pole, extending through about one-fifth of the circumference. Before this furrow has proceeded further a second furrow is formed at right angles to it. The next stages have not been observed, but on the third day after impregnation (fig. 58), the animal pole is completely divided into small segments, which form a disc similar to the blastoderm of meroblastic ova; while the vegetative pole, which subsequently forms a large yolk-sack, is divided by a few vertical furrows, four of which nearly meet at the pole opposite the blastoderm. The majority of the vertical furrows extend only a short way from the edge of the small spheres, and are partially intercepted by imperfect equatorial furrows. The stages immediately following the segmentation are still unknown, and in the next stage satisfactorily observed, on the fifth day after impregnation, the body of the embryo is distinctly differentiated. The lower pole of the ovum is then formed of a mass in which no traces of segments or segmentation furrows can be detected. The embryo (fig. 59) has a dumbbell-shaped outline, and is composed of (1) an outer area, with some resemblance to the area pellucida of an avian embryo, forming the lateral part of the body; and (2) a central portion consisting of the vertebral plates and medullary plate. The medullary plate is dilated in front to form the brain (_br_). Two lateral swellings in the brain are the commencing optic vesicles. The caudal extremity of the embryo is somewhat swollen. [FIG. 59. SURFACE VIEW OF A LEPIDOSTEUS EMBRYO ON THE FIFTH DAY AFTER IMPREGNATION.