The Muscular System is highly symmetrical, and consists of a series of lateral muscular bundles corresponding in number, size, and position to the vertebrie of the chords dorsalis, and bearing a general resem blance to the lateral muscles of the higher fishes. Muller classes the muscles of the Lancelet under the heads of—lat,lateral muscles ; 2nd, abdominal muscles; 3rd, muscles of the oral ring and tcutseula; 4th, muscles of the ring between the oral cavity and branchial sac ; and, 5th, muscles of the branchial apparatus. The skin is thin, tough, and scaleless.
I labita.—The Lancelet lives in sandy ground at a depth of between 10 and 20 fathoms water. It probably buries itself in the san(L When taken it swims rapidly with n snake-like motion, but after a time settles down, unless disturbed, lying flat on its side. It is very tenacious of life. Wo have had it for three hours in a watch-glass under the microscope, at the end of which time when disturbed it seemed as lively as at first. It dislikes the light. It bears handling without injury. Its food was found by Muller in the intestinal canal of some of the specimens he exathined: it consisted of infusorial animalculie. The Lancelet does not swallow but simply imbibes its food.
General Remarks.—"Branchiostonia," says "is evidently a vertebrated animal and a fish. It is distinguished from all other Veriebrata by its peculiar circulatory system, and by the absence of n distinction between the brain and spinal marrow ; from all other fishers by the extraordinary number of branchial ribs, by the union of tho brnnchial and ventral cavities, and by the combination of the respira tory opening with the ventral opening." Mtiller considers it connected with the Cyclostomatous fishes through the peculiar characters of its chordn dorsalis and the absence of jaws, but as inferior to than in the absence of a distinct brain and in the peculiarities of its respira tory system. "The Brenchiostoma," lie concludes, "ranks next the Cyclostomatous fishes, but not among them, being removed from them by distinctions which are greater than the differences between fishes and naked amphibia."
"Viewed SS entire animal," writes Mr. Goodsir, "the Lancelet is the moat aberrant in the vertebrate sub-kingdom. It connects the Vertebrate not only to the Annulose animals, but also through the medium of certain symmetrical A scidim (the genus Pelonaiq of Forbes and Goodsir) to the Mollusks. We have only to suppose the Lancelet to have been developed from the dorsal aspect, the seat of its respi ration to be transferred from its intestinal tube to a corresponding portion of its skin, and ganglia to be developed at the points of junction of one or more of its anterior spinal nerves, and inferior branch of its second pair, to have a true Annulose animal, with its peculiar circulation, respiration, generative organs, and nervous system, with supra-cesophageal ganglia and dorsal ganglionic recur rent nerve." Taking all we know of the structure of this truly wonderful animal into consideration, we are inclined to regard it as the relic of some great order of Fishes, which in their organisation brought down the Vertebrated series to a parallel with the lower forms of Mollv-tca, and which became extinct in some former epoch of the world's geological history, and from the unpreaervable character of their bodies, and absence of hard parts, left "not a wreck behind." The more we know of nature the more are we convinced that there are no isolated organ isms ; that beings apparently anomalous are members of orders either partially known or for the most part extinct. Of all anomalous crea tures the Branchiostoma is the most so, and it is much mere consistent with the principles of scientific zoology to admit it as the type 'of a distinct order among fishes than to attempt to place it among defined groups. The strange combination of characters which it presents—a vertebrated animal without a brain, having the respiratory apparatus of an Ascidian Mollusk, and a ciliated intestinal cavity—if it does almost warrant its erection into the type of a class by itself, certainly is sufficient and more than sufficient to constitute it the type of an order in the lowest of the vertebrate classes.