CYTO-EMBRYOLOGICAL STUDIES OF SEA URCHINS. III. ROLE OF THE SECONDARY MESENCHYME CELLS IN THE FORMATION OF THE PRIMITIVE GUT IN SEA URCHIN LARVAE

¹ Biology Department, Tokyo Metropolitan University, Tokyo, and Misaki Marine Biological Station, Miura-Shi, Japan

1. The first half of the gastrulation process in sea urchins begins with an in toto invagination of the endodermal plate, followed by its stretching.

2. In the second half of the process, pseudopodia are sent out by the secondary mesenchyme cells toward the animal pole. These pseudopodia attach to the blastular wall and pull the archenteron up toward that pole.

3. The pulling capacity of the pseudopodia is shown by the displacement toward the secondary mesenchyme cells of oil droplets injected in the blastocoel.

4. When the pseudopodial connection is artificially severed by one of the following methods, exogastrulae result:

a) Blastocoelic expansion after sucrose treatment (Mespilia globulus, Clypeaster japonicus).

b) Ca-low treatment (Clypeaster, Pseudocentrotus depressus).

c) Pancreatin treatment (Mespilia).

5. Abnormal invagination in various degrees brought about by the above treatments can be accounted for by differences in their effects on the pseudopodia formation.

6. Pseudopodia of the secondary mesenchyme cells are indispensable in the latter half of the gastrulation process in order to produce normal embryos.

This article has been cited by other articles:

				L. Davidson, M. Koehl, R Keller, and G. Oster How do sea urchins invaginate? Using biomechanics to distinguish between mechanisms of primary invagination Development, January 7, 1995; 121(7): 2005 - 2018. [Abstract] [PDF]