. Biological structure and function; proceedings. Biochemistry; Cytology. 5o6 T. GUSTAFSON ectoderm—the "template" [5]. The attachment of the cells to the ecto- derm do not appear to be permanent, however. Preliminary observations indicate that the contacts have a rather restricted life time, and the mesen- chyme cells may thus change their distribution as a response to a further elaboration of the pattern of stickiness of the ectoderm. I may finally mention that the adhesion between the primary mesenchyme and the ectoderm may be determined by the same factor that determines the adhe
. Biological structure and function; proceedings. Biochemistry; Cytology. 5o6 T. GUSTAFSON ectoderm—the "template" [5]. The attachment of the cells to the ecto- derm do not appear to be permanent, however. Preliminary observations indicate that the contacts have a rather restricted life time, and the mesen- chyme cells may thus change their distribution as a response to a further elaboration of the pattern of stickiness of the ectoderm. I may finally mention that the adhesion between the primary mesenchyme and the ectoderm may be determined by the same factor that determines the adhesion between the cells within the ectoderm: The primary mesenchyme cells thus seem to accumulate in those regions where the ectoderm cells. Fig. 7. Primary mesenchyme cells with exploring thin pseudopods (filopods). Drawing from a time-lapse film of a young gastrula. The mesenchyme cells have already arranged themselves into a ring (part of which is seen in the Figure) but still explore the ectoderm in regions far outside the ring level. will come close together (become more or less cylindrical), to form ciliated bands. The phenomenon of random exploration is also applicable to the pseudopods formed by the secondary mesenchyme and the coelomic sacs. As a general conclusion of this brief review we may state that the morphogenesis of the sea urchin larva, in spite of its relative complexity, is not completely obscure but appears to be resolvable into a restricted number of morphological cellular activities, which appear to be released according to a simple time-space pattern, as a wave proceeding from the lower (vegetal) pole towards the higher (animal) pole. The activities in the different zones bear a certain relationship to each other, the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original IU
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