The Reproductive System and associated organs of the Brittle-star Ophiothrix fragilis.

Abstract

ABSTRACT The organs associated, either directly or indirectly, with reproduction in the Ophiuroidea are the axial organ and related sinuses (axial organ complex), the genital rachis, the gonads (localized expansions of the rachis), the gonoducts, and the genital bursae. Evidence is presented in favour of the view of Fedotov (1924) that the axial organ of Ophiuroids is made up of two closely associated parts each surrounded by its own sinus from the wall of which it is, during development, proliferated. The left axial sinus (aboral in the adult) is derived from the left anterior coelom of the larva, the right axial sinus (oral in the adult) from the madreporie vesicle which itself is a derivative of the right anterior coelom of the larva. The ampulla of the stone canal is continuous with, and is part of, the left axial sinus. An account is given of the morphology and histology of the genital rachis and sinus. Examination of the gonads of female Ophiothrix indicate that the breeding season extends from about March to October and that, during this time, there is periodic emission of ova, probably at monthly intervals. Males, on the other hand, produce sperm all the year round. The genital bursae number two pairs to each interradial pouch. They serve, primarily, as organs of respiration. Special mechanisms, which are described, are concerned in the intake and expulsion of water. The gonads do not discharge their products directly into the genital bursae nor through temporarily formed pores in the body-wall but through specially developed and permanent gonoducts, one to each of the ten gonads. Young specimens found in the genital bursae have attained their position only after a period of free-swimming larval life. After settling and metamorphosing, some of the young individuals crawl into the bursae. As a consequence of the previous observation it is pointed out that the presence of the young within the genital bursae of the adult is by no means an indication of a viviparous habit.