THE ACROSOME FILAMENT AND SPERM ENTRY IN THYONE BRIAREUS (HOLOTHURIA) AND ASTERIAS

¹ Department of Biology, Queens College, Flushing, New York and The Marine Biological Laboratory, Woods Hole, Mass.

1. As shown by quantitative data, spermatozoa of Thyone briareus treated with egg water or alkaline (ammoniated) sea water undergo an acrosome reaction resulting in the production of acrosome filaments in a percentage significantly greater than found in untreated controls. Acrosome filaments are also found in inseminated cultures of eggs, either associated or unassociated with the eggs.

2. The acrosome filaments of Thyone briareus are exceptionally long and may even exceed the thickness of the jelly hull (55 µ) or even the length of the flagellum (60 µ).

3. Reacted spermatozoa of Asterias forbesii and A. vulgaris seen in inseminated cultures of eggs have acrosome filaments measuring about 15-22 µ.

4. The general nature of the acrosome filament is much the same in both species of Asterias and in Thyone, regardless of the stimulating agent. Though thread-like in dimensions it is usually straight, or curved only in a wide arc. However, it is capable of curving sharply, bending and perhaps even breaking. The tip or distal portion often sticks to the glass of the slide.

5. At sperm entry in Thyone and Asterias the acrosome filament makes the initial contact with the egg and then enters the egg as the first element of the spermatozoon of which it is an integral part. In Thyone the cone is sometimes so slender as to appear filamentous itself, even though it contains the acrosome filament.