. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. IN SPIROCODON 413 siderable care must be exercised to ensure the presence of freshly shed sperm in the sea water into which the eggs are to be shed. As soon as eggs were observed in the container, a sample was removed to a slide and observed with tin- phase contrast microscope. Mature, unfertilized eggs (Fig. 1) are slightly oval with a depression at the animal pole, where the polar bodies have just been extruded, and at the base of which the pronucleus lies in contact with the egg surface. One or b
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. IN SPIROCODON 413 siderable care must be exercised to ensure the presence of freshly shed sperm in the sea water into which the eggs are to be shed. As soon as eggs were observed in the container, a sample was removed to a slide and observed with tin- phase contrast microscope. Mature, unfertilized eggs (Fig. 1) are slightly oval with a depression at the animal pole, where the polar bodies have just been extruded, and at the base of which the pronucleus lies in contact with the egg surface. One or both of the polar bodies may sometimes be found still adhering to the polar region, although these are usu- ally lost in the course of shedding and the handling of the eggs prior to observation. There are no enveloping layers or membranes, so far as can be determined, either before or after FIGURE 1. Mature unfertilized egg of Spirocodon The egg pronucleus lies at the base of a slight depression left after the extrusion of the second polar body. The fertilizing spermatozoan invariably enters the egg in the immediate vicinity of the egg pronucleus. Further evidence for the existence of some sort of specific attraction on the part of the egg pronucleus for the free-swimming spermatozoa is found in the fact that excess sperm are found only around the animal pole of mature eggs, even in the case of eggs which have been rendered unfertilizable by contact with sea water before the addition of sperm suspension. Immediately after the penetration of the sperm head into the egg cortex, there develops, around the sperm tail, a tubular structure (Fig. 2a) which gradually in- creases in both length and diameter for about five minutes (Fig. 2b-e), while the sperm tail, which maintains slight but continuous movement, is steadily being drawn into the egg. The walls of this "fertilization tube" are entirely transparent, and the sperm tail is perfectly visibl
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
