The blood which circulates through them will consequently be returned in a perfectly aerated condition, to be mixed, however, with that in a less pure state from the visceral lacunes, before it enters the heart. This mixed state of the blood is not by any means peculiar to these animals; for it obtains in many of even the higher Mollusks.

(1356). Nervous System

As in all true Mollusks, the ganglionic centres are placed in connexion with a nervous collar surrounding the oesophagus. In Waldheimia australis the collar is situated at the commencement of the alimentary tube; and there are five nervous centres, three of which, on account of their superior size, may be assumed to be the principal oesophageal ganglia, from which nerves are given off to supply the pallial apparatus, the muscles, and the various viscera of the body.

(1357). No special organs of sense have yet been observed; indeed, sight, hearing, or smell could be of little use to animals like the Bra-chiopods, deprived of locomotion, and firmly fixed during the whole period of their lives to one spot. Forbes and Hanley, in their 'British Mollusca,' regard as ocelli and otolitic capsules certain red spots, perceptible in some species at the bases of the setigerous follicles; but these Mr. Hancock thinks are nothing more than glandular matter in connexion with the growth of the setae.

(1358). The Reproductive system of the Brachiopoda has been minutely described by Mr. Albany Hancock in the memoir above quoted. In Waldheimia australis the generative organs consist of thick bands somewhat convoluted and ramified; they are of a full yellow colour, and are lodged in the trunks and main branches of the great pallial sinuses. There are four of these bands, two in each lobe: those in the dorsal lobe are single, and occupy the two outer or lateral sinuses, extending from behind the attachment of the occlusor muscles to within a short distance of the anterior margin of the mantle;. their posterior extremities reach to the perivisceral chamber. The ventral pair extend as far forward as the dorsal, and are double, that is, each forms a loop, the free extremities of which pass into the outer and inner sinuses of the same side; the looped portions lie within the perivisceral chamber. These genital bands are attached to the inner lamina of the mantle throughout their whole extent by a membrane which, originating in this lamina, passes into a groove extending along the under surface of the genital band. The genital or pallial artery runs along the edge of this membrane, and has the reproductive organ developed around it.

This is the most obvious disposition of the parts, as apparent on a general examination; but on a closer inspection, there can be but little doubt that these organs are in reality developed between the two membranes which compose the inner lamina of the mantle, and, bulging out the interior of these, become suspended, as it were, in the pallial sinus. Those in which ova are deficient are generally supposed to be the male secreting organ. The form, colour, and general appearance of these eggless bands do not differ, however, from those charged with ova, and have very-much the character of undeveloped ovaries. The generative organs are very perceptibly composed of two elements - the yellow ovigerous substance, which forms the chief mass, and a red material, which is distributed over the surface of the organ. When the organ is in a low state of development, this red matter forms a narrow irregular cord, which runs along the sides of the band, and is occasionally spread over the surface in spots and blotches. When the ova are mature, this substance can still be traced as small specks on the surface and throughout the mass.

From what will shortly be stated in regard to Lingula, it seems probable that this red matter may prove to be the testis.

(1359). The minute structure of these organs has not been sufficiently examined; it may be stated, however, that the ova appear to be developed in cells, and that when the yellow mass which is deficient of eggs is broken up and placed under the microscope, it is found to be composed almost entirely of minute clear granules. The red substance is likewise made up of large irregular cells inclining to oval, very variable in size, and without any apparent nucleus.

(1360). In Lingula the reproductive organs are withdrawn altogether from the mantle, and placed in the perivisceral cavity: they are very bulky, occupying a large portion of the chamber; they lie for the most part behind the liver, and surround the alimentary tube; they form four irregularly lobulated branched masses, two above and two below the tube; these pairs may be denominated the dorsal and ventral ovaries. When in a highly developed state, the lobes or branches insinuate themselves between and around the muscles, so that it is almost impossible to trace the relation of these organs to other parts; but when immature it is very easy to do so. The dorsal ovaries are then found to be suspended by the ilio-parietal bands, the ventral by the continuation of these bands along the pseudo-hearts or oviducts. In both cases the attachment is along the margin of the bands, between the two layers of which they would seem to be developed. In Lingula the red substance alluded to above forms a dendritic or branched organ, spread over the external surface of the ovarian masses.

On examining a portion of this branched organ under the microscope, it is found to be composed of large irregular cells, somewhat elliptical in form, and closely resembling those of the red substance in connexion with the ovaries in Waldheimia. The cells, however, in Lingula appeared to present different stages of development, varying much in size and form, and some of them were filled with numerous delicate hair-like bodies resembling spermatozoa. From these facts it can scarcely be doubted that the dendritic organ is the testis, and that the fusiform cells are fully developed spermatophora containing spermatozoids. It would thus appear that Lingula is androgynous: and if the red matter in connexion with the generative organs in the articulated Brachiopods should prove to be the same as the dendritic organ in the former, then in them also the sexes are combined.

(1361). Professor Owen supposed that the ova, when mature, escape by the dehiscence of the pallial membranes. So long as no passage was discovered leading externally from the perivisceral chamber, this could be the only possible conclusion, but can now be no longer maintained, for it has been ascertained that more than one such passage exists. The natural inference would therefore seem to be that the eggs will find their way through these passages, which may consequently be looked upon as oviducts.

(1362). These curious organs were originally described by Cuvier as hearts, in his well-known memoir on Lingula anatina, and subsequently by Professor Owen on the Brachiopoda generally; they open, however, externally, and therefore can have nothing to do with the vascular system.

(1363). In Lingula the oviducts are rather peculiar in form, though essentially the same as in the articulated Brachiopods. They are two in number, and lie to a great extent between the two layers of the ilio-parietal bands, stretching along the lateral walls of the perivisceral chamber from the front to behind the dorsal attachment of the adjuster muscles, and are so concealed by the viscera and muscles that very little of them can be seen until these parts are removed. The expanded portions open upwards and towards the lateral walls of the body, through the processes of the ilio-parietal bands, close to the side-walls of the chamber. They are of a yellowish colour, and terminate at the external surface in two small diagonal slits, one a short way on either side from the median line, a little below the mouth. The walls have a glandular appearance, the inside being velvety from the numerous minute villi which crowd the surface.

(1364). From the nature of these organs, it seems probable that the ova on their passage outwards may receive some external covering. In two instances in which the ova were mature, Mr. Hancock found them in vast numbers strewed about the perivisceral chamber, and in one of the oviducts several had penetrated nearly to the external orifice.