Organisation. Skeleton.—The osseous system consists of a chords dorsalis tapering at both ends, and, strange to say, not prcsenting.tho slightest vestige of a cranium, and of the germs of superior and inferior inter-spioous bones and fiu-rays in the most rudimentary state. The chords dorsalis is composed of from 60 to 70 vertebrae.
which are also in a rudimentary state, and little more than indicated. "The chords dorsalis," to quote Mr. Goodsir, "is formed externally of a fibrous sheath, and internally of an immense number of latninie, each of the size and shape of a section of the column at the place where it is situated. When any portion of the column is removed these plates mOy be [mailed out from the tubular sheath like n pile of coins. They have no groat adhesion to one another, are of the consistence of parchment, and appear like flattened bladders, DA if formed of two tough fibrous membranes pressed together." Besides the skeleton of the nervous system there is a hyoid apparatus forming the armature of the mouth, and consisting of two rots of 17 articu• lated pieces, from each of which, except two, a ray proceeds. These rays form the oral cirrhi. Muller takes n different view of this structure, maintaining that it corresponds neither to the jaw-bone nor to the hyoid apparatus in other animals, but is analogous to the cartilaginous ring of the mouth of the lamprey and the Myxinoid fishes, a system peculiar to that family. There is also in the Lan celet n series of fine, transparent, cartilaginous, hair-like ribs, 70 to 80 on each side, forming a cage for the protection of the branchial cavity.
Nervous System.—The spinal cord extends the whole length of the spine, but is not quite so sharp at the fore-end as behind. It presents no trace of a brain. From 55 to 60 nerves pass off from each side of it, which do not arise by double roots. The details of this important part of the animal's anatomy are fully given by Mr. Goodsir. Muller and Itathke have observed the existence of rudi mentary eyes, consisting of n small black spot of pigment, but not furnished with any optical apparatus. No traces of organs of smelling or hearing have been met with.
Vascular System.—The observations of Muller having been made on the living animal, he was enabled to pursue this part of its organisation further than the other observers. According to him
the vascular system of this animal corresponds in general arrange ment with that of fishes, differing however in regard to the heart from that of all other vertebrate animals, and displaying a striking accordance with that in worms ; for the hearts in the Branchiostoma are not only more divided than in other animals of its class, but present entirely the form and distribution of blood vessels, and extend over wide spaces. The blood is white.
The Respiratory System is constituted by the anterior extremity of the intestinal tube, the walls of which are clothed with vibratile cilia, and protected and adapted to their office by the peculiar cage like skeleton already mentioned, which is further strengthened by transverse cartilaginous rods, between which are numerous clefts, their openings protected by vibratile cilia. This was first made known by Muller, who described also a curious apparatus of finger shaped wheel-organs and fringed folds placed at the entrance of the branchial cavity, and marking the commencement of the ciliated portion of the intestinal canal of which the branchial sac forms n part. At the end of the branchial sac is the porus abdominalis, an opening which serves equally respiratory and genital purposes.
The Digestive System consists of an intestinal canal and a eceelim, both of which are ciliated. The latter is considered by Muller to be a liver, but the office of a liver appears to be performed equally by the other parts of the intestines.
The Reproductive System is imperfectly known. As far as it has been observed it appears in the form of certain bean-shaped bodies attached to the inner surface of the lining of the abdomen on the out side of the branchial canals. Miiller distinguishes the two sexes, but this part of the history of the Lancelet demands further investigation. It is not impossible that the two membranous folds of the abdomen and their canals may be connected with this system, and serve mar supial purposes. This remark, however, we merely throw out as a suggestion.