Smaller Blastomeres Research Articles

SPICULE FORMATION IN VITRO BY THE DESCENDANTS OF PRECOCIOUS MICROMERE FORMED AT THE 8-CELL STAGE OF SEA URCHIN EMBRYO.

The micromeres at the 16-cell stage of sea urchin embryo have already been endowed with a faculty to self-differentiate into spicule-forming cells (11). The present experiment was designed to test whether the factor(s) necessary for such self-differentiation had already been localized at the 8-cell stage in an area corresponding to the presumptive micromere region in Hemicentrotus pulcherrimus. Since the blastomeres at the 8-cell stage are all equal in size in normal embryo, unequal 3rd cleavage, by which small blastomeres are pinched off toward the vegetal pole (precocious micromeres), was experimentally induced either by treatment with 4NQO (4-nitroquinoline-1-oxide) at the 2-cell stage or by continuous culture in Ca-free sea water. The precocious micromeres were cultured in vitro in natural sea water containing horse serum. Descendants of the precocious micromeres formed spicules. In comparison their spicule formation with that by the descendants of the micromere of normal embryo, no differences were found regarding 1) time of initiation of spicule formation, 2) rate of growth of spicule, 3) size and shape of resultant spicule and 4) percentage of clones which formed spicule. The fact indicates that factor(s) indispensable for self-differentiation into spicule-forming cells have already been localized near the vegetal pole as early as the 8-cell stage.

A scanning electron microscope study of the hatching of bovine blastocysts in vitro

The blastocysts were recovered from cows 7--10 days after oestrus and cultured. The zona pellucida has a spongy fibrous structure. Hatching begins, about 24 h after culture, through a relatively small hole out of which the blastocyst appears to escape by its own activity. Later the zona becomes split and the two edges of the slit surround part of the blastocyst. The emerging cells were large or small blastomeres which were generally covered by a dense mass of microvilli.

MALATE DEHYDROGENASE: MULTIPLE FORMS IN SEPARATED BLASTOMERES OF SEA URCHIN EMBRYOS.

Sea urchin embryos at the 64-cell stage were dissociated by treatment with trypsin and separated by centrifugation on a sucrose gradient. The large blastomeres have two and the small blastomeres have three bands of L-malate dehydrogenase activity, which are separated by disk microelectrophoresis on polyacrylamide gel, whereas unfertilized eggs have five.

Studies on the Onychophora VII. The early embryonic stages ofPeripatopsis, and some general considerations concerning the morphology and phylogeny of the arthropoda

Studies on the Onychophora VII. The early embryonic stages of<i>Peripatopsis</i>, and some general considerations concerning the morphology and phylogeny of the arthropoda

THE RELATION BETWEEN ENTRANCE POINT OF THE SPERMATOZOÖN AND BILATERALITY OF THE EGG OF CHÆTOPTERUS

Previous articleNext article No AccessJournal ArticlesTHE RELATION BETWEEN ENTRANCE POINT OF THE SPERMATOZOÖN AND BILATERALITY OF THE EGG OF CHÆTOPTERUST. H. MORGAN and ALBERT TYLERT. H. MORGAN Search for more articles by this author and ALBERT TYLER Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Biological Bulletin Volume 74, Number 3June 1938 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.2307/1537813 Views: 4Total views on this site © 1938 Marine Biological LaboratoryPDF download Crossref reports no articles citing this article.

OBSERVATIONS ON REPRODUCTION, PREMATURATION, AND FERTILIZATION IN SABELLARIA VULGARIS

1. Sabellaria vulgaris, a polychæte annelid inhabiting sand tubes on dead Echinarachnius and other shells in Bryozoa nodules, and on stones, occurs abundantly in the vicinity of Woods Hole, Mass., and gametes may be secured throughout the summer months. Shedding takes place immediately following the removal of the animals from their tubes.2. The early development is described from shedding to early cleavage and a comparison made with Sabellaria alveolata as described by Fauré-Fremiet. In most respects the early developmental phenomena of these two species are strikingly similar.3. After shedding the eggs become spherical, the vitelline membrane elevates, leaving fine protoplasmic processes between membrane and egg cortex, and the contents of the germinal vesicle form a clear area at the animal pole. Visible polarity appears during pre-maturation which ceases at the metaphase of the first maturation spindle.4. It is said that fertilization occurs normally during May and June but a second and shorter time has been found during the early part of August. During July a high percentage of fertilization may be secured with slightly alkaline sea water (8.6).5. The highest percentage of cleavage is obtained when the gametes are shed together. Eggs may be fertilized after seven hours, but the fertilizing capacity of the spermatozoa is considerably shorter (about one hour).6. The fertilization phenomenon is described. The protoplasmic strands serve to transmit the stimulus of sperm contact. No fertilization membrane appears and the first indication that a spermatozoön has entered is the withdrawal of the processes.7. The fertilization cone is enormous and changes shape. Spermatozoa may enter at any point on the periphery but more frequently in the animal hemisphere. The polar bodies are large and the first one frequently divides.8. Various factors such as increase of pH, shaking, and standing are sufficient to disturb the equilibrium of the pre-maturation spindle with the resultant formation of one or two polar bodies. This is followed by lobular fragmentation and no swimming embryos develop. Old unfertilized eggs stratify into three zones.9. Plane of first cleavage bears no fixed relationship to sperm entrance point and passes to one side of pole as determined by the position of the polar bodies. The polar bodies lie on the smaller blastomere while the larger one contains the polar lobe material.