The works of Francis Maitland Balfour, Volume 3 (of 4)

by Francis M. Balfour

Chætopoda.—Lumbricus, &c.

Discophora.

It is very possible that the cases quoted under this head ought more properly to belong to group 1.

4. The mesoblast cells are split off from the epiblast.

Nemertea.—Larva of Desor. The mesoblast is stated to be split off from the four invaginated discs.

5. The mesoblast is split off from the hypoblast.

Nemertea.—Some of the types without a metamorphosis.

Mollusca.—Scaphopoda. It is derived from the lateral and ventral cells of the hypoblast.

Gephyrea.—Phascolosoma.

Vertebrata.—In most of the Ichthyopsida the mesoblast is derived from the hypoblast ([fig. 213]). In some types (i.e. most of the Amniota) the mesoblast might be described as originating at the lips of the blastopore (primitive streak).