Volume 1

The works of Francis Maitland Balfour / edited by M. Foster and Adam Sedgwick.

  • Balfour, Francis M. (Francis Maitland), 1851-1882.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: The works of Francis Maitland Balfour / edited by M. Foster and Adam Sedgwick. Source: Wellcome Collection.

    927/948
    The first drawing (fig. 37), viz. that of the whole embryo, shews an embryo of an oval shape, possessing six somites, whilst along the middle of its ventral surface there are two slit- like openings, lying parallel to the long axis of the body, and placed one behind the other. The mesoblastic somites are ar- ranged bilaterally in pairs, six on either side of these slits. The following note in his handwriting is attached to this drawing: Young larva of Peripatus capcnsis.—I could not make out for certain which was the anterior end. Length i'34 milli- metres. Balfour's three remaining drawings (figs. 40—42) are, as already stated, representations of transverse sections of the embryo figured by him as a whole. They tend to shew, as he stated in the letter referred to above, that the mesoblast originates as paired outgrowths from the hypoblast, and that these outgrowths are formed near the junction of the hypoblast with the epiblast at the lips of the blastopore. In fig. 42 the walls of the mesoblastic somites appear con- tinuous with those of the m.esenteron near the blastopore. In fig. 40, which is from a section a little in front of fig. 42, the walls of the mesoblastic somites are independent of those of the mesenteron. Fig. 41 is from a section made in front of the region of the blastopore. In all the sections the epiblast lying over the somites is thickened, while elsevv^here it is formed of only one layer of cells; and this thickening subsequently appears to give rise to the nervous system. Balfour in his earlier investigations on the present subject found in more advanced stages of the em- bryo the nerve-cords still scarcely separated from the epiblast \ We have since found, in Balfour's material, embryos of a slightly different age to that just described. Of these, three (figs. 34, 35, 36) are younger, while one (fig. 38) is older than Balfour's embryo. Stage A.—The youngest (fig. 34) is of a slightly oval form, and its greatest length is 48 mm. It possesses a blastopore, ^ Comparative Embryology, original edition, Vol. i. p. 318. [This edition, Vol. ii. p. 385-] 58—2