OBSERVATIONS ON REPRODUCTION, PREMATURATION, AND FERTILIZATION IN SABELLARIA VULGARIS

¹ From the Department of Biology, Brooklyn College, and the Marine Biological Laboratory, Woods Hole

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.