The ova of Ascidice, instead of passing from the ovary to the branchim, there to be deve loped as in a uterus, are emitted externally, by the oviduct conveying them into the cloacal cavity, whence they arc carried outwardly by the current of water through the external anal aperture, or through the communicating lateral opening into the branchial sac, and thence through the branchial aperture. Cuvier says that he found some minute egg-like bodies between the branchial sac and the mantle ; a position very analogous to that held by the ova of the bivalve Molluscs ; and he thought it probable that ova so placed were fecundated by seminal fluid emitted by the same duct that leads from the ovary. These granules, however, M. Savigny appa rently regards as little glands.
The generative organs are sometimes single and sometimes double ; in the latter case, the two halves, right and left, are completely se parate, as in other Acephalans, and emit their products separately into the cloaca, which serves as a kind of incubational or marsupial pouch.
The ovary is single in Phallusia, Pandocia, and Dendrodoa ; it is usually double in Bol tenia, &c. In Cynthia the ovary is either single or multiple, sometimes very large, form ing long groups of clustered globules, each globule being crowded with ova.
The single ovary is sometimes enclosed within the intestinal loop, without adhering to it, and sometimes, as in C. papillata, &c., it lies against, and is adherent to, the rectum. In C. papillate the ovary is bent on itself and terminates by an oviduct at each end. In C. canopus there are 2-4 or more ovaries ; those on the right side are placed against the rectum, and all terminate, as usual, by oviducts. In C. microcosms there are two ovaries on the left side. They are composed of separate gelatinous lobes, having the appearance of a bunch of grapes. In C. mytiligera the ovary has the form of a membranous pouch, which furnishes points of attachment to the exterior of the branchial sac, and is fixed to the mantle and to the inner part of the intestinal loop. Its duct is very thin, and follows the usual course by the side of the rectum. In C. polycarpa and C. pomaria, Savigny describes certain numerous hemispherical or conical bodies adhering to the mantle, almost fifty in number, and disposed in rows, somewhat cor responding to the six branchial folds, as being possibly the ovaries of these species. These bodies are without ducts ; they are formed of a mass of granules resembling the eggs of some other Ascidians ; they are much com pressed, and resemble a compound berry held in a 5-fid cup ; they have apparently no com munication with each other or externally, and are accompanied at their base with gelatinous, transparent, subpedunculated vesicles, appa rently empty. In C. papillata, which has other generative organs, there are many rows of isolated, gelatinous, semitransparent, wrinkled vesicles, corresponding to the arrangement of the branchial folds, attached to the mantle, and receiving bloodvessels from it. The lobes of the ovary in C. microcosmus, after the emis sion of the eggs, wither into wrinkled vesicles closely resembling these sessile vesicles in C. papillate. Certain soft bodies observed in C. microcosnzus, and somewhat similar to the above, Cuvier regarded as fat, serving as stores of nutritive matter ; but with this Savigny cannot agree. Savigny also points out the occurrence of various irregular, but somewhat similar fungous or fleshy excrescences on the mantle ( fig. 39. i,/, Vol. I. p. 112.), ovaries, and intestines, sometimes even quite investing the latter ; but these are quite distinct from the ovary-like bodies above described.
In Boltenia reniformis the ovaries are double, unequal in size, elongate, formed of coarse subcubical lobes, situated one on each side of the body, and directed towards the anal orifice; the right or smaller ovary, straight, claviform, fitting closely into the ascending loop formed by the stomach and intestine. The left ovary, larger and less lobulated, is on the opposite side, between the mantle and the branchial sac - it is undulating, and extends downwards behind the branchial vein. The tissue of these ovaries is a yellowish membrane of distinctly cellular structure, containing groups of large opaque ova and smaller clusters of exceedingly minute diapha nous granules. The ovaries of Cystingia are two free racemes composed of globular bodies, as in Cynthia., arranged on the two sides of the body with the branchial sac and stomach between them. In Dendrodoa ( fig. 778. k) the ovary is single and branched, consisting of a trifurcate, cylindrical stem, bearing at its base on one side a forked branch, and on the other a simple one, all of the same thickness ; it is situated on the left side of the body between the mantle and the branchial sac. In Chelyosoma, Professor Eschricht de scribes as an ovary two darkish bodies, filled with vascular ramifications ; placed, one be tween the liver and the rectum, and the other around the fold of the intestine. Another somewhat similar organ, traversed by rami fying vessels, and placed at the anterior ex tremity of the body, is apparently the testicle. Connected with this organ, a distinct sigmoid duct runs to the right posterior angle of the body, from whence a filamentous tube passes along to the left posterior corner.* In Cynthia ampulla the generative organs are situated in the intestinal fold, and appear at first sight to form a single organ ; but by the aid of the mi croscope two distinct organs, male and female, are easily recognised (fig. 779. A). The testicle forms a sort of framework around the ovary ; it is of a milky white colour, and is composed of an infinite number of short, twisted caeca, visible to the naked eye, and somewhat ana lomous to the seminiferous canals composing the testicles of higher animals. Three or four mammillary processes rise from the anterior surface of this organ : they are hollow in the centre, and emit a milky fluid, which is shed into the cloaca, and contains, or rather is almost composed of, spermatozoa, with dis eiform heads and filamentous tails. The ovary is blackish, and is situated in the midst of the testicle. Its situation corresponds to that of the ovary of the Limaces among the Gasteropods, which is surrounded by the liver. It is easily distinguished from the testicle by its colour and by the appearance of its contained eggs. The oviduct opens into the cloaca by the side of the anus. In Ascidia grossularia the eggs, seen through the walls of the ovary, are of a fine red colour, and are contained in separate sacs, the ovary appearing like a bunch of grapes ( fig. 779. a). Van Beneden has distinctly seen in all of these ova the two germinal vesi cles. The vitellus is at first white, but during development it becomes of a deep red. By the side of the ovary is another series of sacs without ova, and some free cells containing a great number of other more minute cells moving about in their interior, and which when shed swarm about like spermatozoa. These appear to constitute the male organ, and its disposition accords with that of the Amaroucium argus, and with that of the Bryozoa (Van Beneden).