- A, reproductive system of Amphilina foliacea: a, glandular pit; b, opening of uterus; b', uterus (black); c, yolk-gland and its duct; d, ovary; e, e', opening and duct of vagina; f, spermotheca; g, male genital opening (gonopore); h, penis; i, vas def erens; j, testes; k, shell-gland.
Outline of the ventral surface to show the external apertures and nervous system; a, rosette-organ; b, uterine pore; c, terminal sucker; e, vaginal pore; g, male gonopore; n, o, p, nervous system.
A single or paired accessory gonopore is met with in many Trematodes just as in certain Turbellaria (e.g.
In this group, the accessory gonopore is the opening of the "vagina," in contradistinction to the median and atrial opening of the uterus which is a "birth-pore."
In most endoparasitic Trematodes the accessory gonopore is a median and dorsal structure.
The comparative anatomy of living forms, combined with the evolutionary hypothesis sketched above, suggests that the early holothurians possessed the following characters: subvective grooves entirely closed; 5 radial canals, proceeding from the water-ring, gave off branches furnished with ampullae to the podia on each side of them, the 10 anterior podia being changed into cylindrical tentacles; the transverse muscles of the body-wall formed a circular layer, probably interrupted at the radii (though Ludwig believes the contrary); longitudinal muscles as paired radial bands, without those special retractors for withdrawing the anterior part of the body which occur in many recent forms; a hydropore connected with the water-ring by a canal in the dorsal mesentery; a gonopore behind the hydropore connected by a single duct with a bunch of genital pouches on each side of the mesentery; gut dextrally coiled, with a simple blood-vascular system, and with an enlargement at the anus for respiration, this eventually producing branched caeca called "respiratory trees"; skeleton reduced to a ring of 5 radial and 5 interradial plates round the gullet, and small plates, with a hexagonally meshed network, dispersed through the integument.