All the Sterelmintha of the Trematode order arc androgynous; but the generative apparatus, instead of being divided and multiplied as in the Tiertire, is individualized, and its several parts receive a higher degree of development. We have selected the figure which Nordmann has given of the Distoma perlatum, on account seen through the transparent integument, c d the windings of the beginning of the simple digestive cavity, c e the two intestinal prolon gations, ff the dilated claviform eceeal ter minations of the intestines, g the two internal, and h. the two external trunks of the vascular system proceeding to the anterior part of the body ; i is the great sacciform uterus, k ap parently glandular bodies contained therein, l an the two testes, which are beset internally with small spines or cilia ; ii the projecting cirrus from which the ova are expelled, o the terminal dilatation of the oviduct which com municates with the testes, p p p p convo lutions of the oviduct which are filled with ova, y q the mass of ova which lies above the ovi duct, and occupies almost the whole cavity of the body, r r the passages by which the ovaries communicate with the uterus or dilated commencement of the oviduct.
The generative organs present some varieties in the.Planariaz, but are essentially the same as in the Distomata. In the Planaria lactea the penis and oviduct are situated below, and the two vesicular and secerning parts of the apparatus towards the upper part of the body. The male organ (a, jig. 92) consists, according of the clearness with which the several parts are delineated, but it must he observed that it deviates in some remarkable peculiarities from what may be regarded as the Trematode type of the reproductive organs.
The specimen is seen from the under side, part of the parietes of the body having been reniosed it is the oral aperture, b the usophagus to the researches of Professor Duges, of two. parts, one of which is free, smooth, semi transparent, contractile, and always divided into two portions by a circular constriction ; it is traversed by a central canal, susceptible of being dilated into a vesicle, and is open at its free extremity, which is turned backwards ; the second division is thicker, more opaque, vesicular, adherent to the contiguous paren chyma, and receives two flexuous spermatic canals (b, b). The free portion of the penis is con tained within a cylindrical muscular sheath (c), which is adherent to the circumference of the baie of the intromittent organ, and serves to protrude it externally. This sheath commu nicates with the terminal sac of the female apparatus near its outlet by a projecting orifice (d). The oviduct (e) opens into the posterior part of the terminal sae : it is a narrow tube which passes directly backwards, and dividing into two equal branches, again subdivides and ramifies amongst the branches of the dendritic digestive organ. Besides the ovary there are
two accessory vesicles (g and h), communicating together by a narrow duct (7), and opening into the terminal generative sac.
Al. Baer twice witnessed the copulation of Planaria in the species Plaimria larva. Upon separating the individuals, he perceived a long white tube projecting from the genital pore of each, proving the reciprocity of fecundation.
Notwithstanding the complicated apparatus above described, the P1unarit are remark able for their spontaneous fissiparous gene ration, and the facility with which detached or mutilated parts assume the form and func tions of the perfect animal. leg. 92, o, repre sents a Planuria laden, with the anterior part of the body artificially divided in the longitu dinal direction ; fig. 92, E, shews the same in dividual having two perfect heads, the result of the preceding operation. • The female generative organs of the Lingua tula ( Perttastonia) tornioidcs _present a struc ture in some respects analogous to that of the Disloma perlatum : the ovary (n, n, Jig. 78) is a part distinct from the tubular oviduct, and is attached to the integument or pa rictes of the body, extending down the middle of the dorsal aspect. It consists of a thin stratum of minute granules; clustered in a ramified form to minute white tubes, which converge and ultimately unite to form two oviducts (a, a, jig. 78). These tubes pro ceed from the anterior extremity of the ovary, diverge, pass on each side of the alimentary canal, and unite beneath the origins of the nerves of the body, so as to surround the oesophagus and these nerves as in a loop. The single tube formed by the union of the two oviducts above described, descends, winding round the alimentary canal in numerous cods, and ter minates at the anal extremity of the body. The single oviduct, besides receiving the ova from the two tubes (o, a), communicates at its com mencement with two elongated pyriform sacs (m, nt), which prepare and pour into the ovi duct an opaque white secretion. These bodies, from their analogy to the impregnating glands in the Trematoda, I was led to regard (in the description, publisl:ed in the Zoological Tntns actions, of the only individual of this interesting species that I have hitherto been able to pro cure for dissection,) as testes, and the gene ration of the Linguatnla to be androgynous, without reciprocal fecundation ; individuals, however, of the male sex have since been de scribed in this species by Miran)* and Diesing.