THE PROCESS OF EGG-LAYING IN THE CHAETOGNATH SAGITTA HISPIDA

¹ Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 33149

1. There is considerable disagreement in the literature concerning the manner in which eggs are fertilized and reach the exterior in chaetognaths, even in studies on the same species. This study makes use of observations on populations of living animals maintained in the laboratory, and of material fixed at known stages of the egg-laying process, and provides photographic evidence to illustrate the points enumerated below.

2. There is a single duct, serving both as an oviduct and sperm duct in the female reproductive system of the chaetognath Sagitta hispida, which runs from the gonopore anteriorly along the outer border of each ovary.

3. Following fertilization eggs slowly pass through the germinal epithelium (crescent) through pores much smaller than their own diameter into this duct, and displace the sperm in it.

4. The eggs, which become cylindrically compressed, are extruded very rapidly from the duct to the exterior by a combination of muscular forces, and deposited in a mucous matrix onto a surface to which the animal is attached.