nilANCHIOSTOMA. 



BRANCHIOSTOMA. 



which are also in a rudimentary state, and little more than indicated. 

 " The chorda donalis," to quote Mr. Ooodair, " is formed externally 

 of a fibrous sheath, and internally of an immense number of lumime, 

 each of the size and shape of a Motion of the column at the place 

 where it u situated. When any portion of the column ia removed 



Explanation of the Figures : 



Fig. 1. The Lancelot, a little larger than life, a, the mouth ; 4, poms 

 abdominslis ; e, the vent. 



fig. 2. View of the animal from beneath, a, the mouth ; i, poriu abdoml. 

 nalis ; c, rent ; d d, ventral folds. 



Fig. S. The neuro-skeleton of the Lancelet, consisting of a, the chorda 

 donalis ; 1 1, the vesicular germs of the dorsal fin-rays ; c, those of the anterior, 

 and d, those of the posterior anal fins (from Goodsir). 



Fin. 4. The intestinal system, a, the branchial sac ; b, the oesophagus ; 

 c, greener and wider part of the intestinal canal ; d, circum ; e, narrower and 

 posterior part of the intestinal canal. 



Fig. S. Anterior extremity of the body of a young animal (from Mllllcr). 

 The lateral muscles are omitted in order to show more clearly the other part*. 

 , chorda dorsatis ; *, its sheath ; c, rounded anterior extremity of the body, 

 terminating in the dorsal fin ; d, cellular dorsal fin-rays ; and e, their contemn ; 

 /, spinal marrow ; A, eye ; i, labial cartilages ; k, ilrrhi of the mouth ; /, a 

 muscle of the labial cartilages, arising from the fringed fold between the cavity 

 of the mouth and branchial cavity ; m, wall of the mouth ; n, finger-formed 

 figures on the wall or the mouth (ciliated organs) ; o, fringed fold between the 

 oral and branchial caviiies ; p, heart-like arch of the aorta, connecting arch 

 between the branchial heart and aorta ; , anterior and superior part of the 

 bi anchial sac. In which the branchial slit* are wanting ; r and , branchial ribs ; 

 (.branchial slits ; , walls of the belly. 



Fig. 0. Transverse section of the body (from Milllor). n, chorda dorsalis; 

 t, Its sheath ; r, membranous layer ; d, spinal marrow, and /, canal above it ; 

 I and *, section of fin.nyi ; i, lateral muscles ; *, intcrmuacular ligament ; 

 /, branchial sac ; m, ovarla ; n, wall of belly ; a, lateral ventral folds, with their 



Flff. 7. View of the anterior part of the body frnm bcnesth. a, mouth ; 

 , drrhl ; <, snout ; rf, ventral wall ; /, lateral ventral fold. 



Fig. . View of the underside of the body In the region of the porus abdomi- 

 nalls. a, ovary ; /, lateral ventral folds ; g, poru abdominal!*. 



them platen may be puahed out from the tubular sheath like a pile 

 of coins. They have no great adln j i"ii to one another, are of the 

 consistence of parchment, and appear like flattened bladders, M if 

 formed of two tough fibrous, membranes; pressed together." Besides 

 the akeleton of the nervous system there u a hyoid apparatus forming 



the armature of the mouth, and consisting of two seta of 17 articu- 

 lated pieces, from each of which, except two, a ray proceeds. These 

 rays form the oral cirrhi. Muller takes a diiVereiit view of this 

 Ntrueture, 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- 

 eelet a 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. 

 Qoodsir. Muller and Rathke have observed the existence of rudi- 

 mentary eyes, consisting of a small black spot of pigment, but not 

 furnished with nny 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 lirrmchiottonw 

 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 HRC forms a 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 coocum, 

 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. Muller distinguishes the two sexes, but 

 this part of the history of the Laneelet demands further investigation. 

 It is not impossible that the two membranous folds of the abdomen 

 anil their canals may be connected with this system, and serve mar- 

 supial purposes. This remark, however, we merely throw out as a 

 suggestion. 



The Muscular System is highly symmetrical, and consists of a series 

 of lateral muscular bundles corresponding in number, size, and position 

 to the vertebra of the chorda dorsalis, and bearing a general resem- 

 blance to the lateral muscles of the higher fishes. Muller classes the 

 muscles of the Laneelet under the heads of 1st, lateral muscles ; 2nd, 

 abdominal muscles ; 3rd, muscles of the oral ring and tentacula ; 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 M ili ]--. 



Habits. The Laneelet lives in sandy ground at a depth of between 

 10 and 20 fathoms water. It probably buries itself in the sand. 

 When taken it swims rapidly with a snake-like motion, but after a 

 time settles down, unless disturbed, lying flat on its side. It is very 

 tenacious of life. We 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 intwtinal canal 

 of some of the specimens he examined : it consisted of infusorial 

 !,riu:ilnil:i?. The Lancelot does not swallow but simply imbibes ita 

 food. 



General Remarks. " Branchiottoma," says Muller, " in evidently 

 a vertebrated animal and a fish. It is distinguished from all other 

 Yerlebrata by its peculiar circulatory system, and by the absence of a 

 distinction between the brain and spinal marrow ; from all "tlier fishes 

 by the extraordinary number of branchial ribs, by the union of the 

 branchial and ventral cavities, and by the combination of the respira- 

 tory opening with the ventral opening." Muller considers it connected 

 wit'], the Cyclostomatous fishes through tin- peculiar rlmrncters of iU 

 chorda dorsalis and the absence of jaws, but ns inferior to them iu 

 the absence of a distinct bruin and in the peculiarities of its respira- 

 tory system. " The Branrliiottoma," he concludes, " ranks next the 

 Cyclostomatous fishes, but not among them, being removal from them 

 by distinctions which are greater than the differences between fishes 

 and naked amphibia." 



