226 



HARD WICKE 'S SCIENCE- GOSSIP. 



It is now proposed to refer to some of the most 1 

 aberrant forms of living fish and their fossil affinities ; 

 then, briefly passing in review tlie distribution of the 

 various families in geological time, to see how far 

 descent with modification is traceable in this class of 

 vertebrates. 



It is well known that the lowest vertebral form is 

 the anomalous lancelet {Amphioxits lanceolatits), 

 which is found burrowing in sandbanks on our south- 

 ern shores and in the Mediterranean. The position 

 which this singular species should occupy in the 

 animal kingdom has long been a subject of debate 

 among naturalists. Some, like Agassiz, separate it 

 entirely from all other fishes, while Haeckel proposes 

 to place it in a distinct division of the Vcrtebrata, and 

 Professor Semper removes it from the vertebrates 

 altogether. But Professors Owen and Huxley, con- 

 sidering it to possess the rudiments of a skull and 

 brain, with the elements of a vertebral column, retain 

 it among the fishes, and it forms the first or lowest 

 orders of their respective systematic arrangements. 

 \v\.Amphioxiis, which ranges from one inch and a half 

 to two inches in length, the vertebral column is noto- 

 chordal throughout life, — that is to say, composed of 

 a membraneous sheath enclosed in cartilage, — and as 

 there is no enlargement of the skull for the reception 

 of the brain, the animal tapers nearly equally at either 

 end. The skin is scaleless, lubricous, and so trans- 

 parent that the internal structure is visible, and the 

 eyes are not more fully developed than in the common 

 leech. The mouth is vertical, jawless, and suctorial, 

 and is furnished with vibratile cilia. The lancelet 

 possesses neither heart nor swimming bladder, and is 

 without ribs and even rudimentary limbs. In all 

 other fishes respiration is effected by means of water 

 passing through the mouth and escaping by the gills, 

 or their equivalents ; in this species it traverses the 

 whole interior of the animal, and escapes by a special 

 pore on the under surface of the body. Prof. Goodsir 

 long ago called attention to this peculiar mode of 

 respiration, and noticed the resemblance between the 

 enlarged pharangeal sac oi Amphioxus and that of the 

 tunicated mollusks or sea squirts. He considered the 

 lancelet also as allied to the annulosa, from the simple 

 organization of its respiratoiy and circulatory system, 

 and M. Kowalevesky has more recently traced a close 

 affinity between this species and the early stages of 

 some Ascidians. Thus, in Amphioxits are vmited 

 characters belonging to the Timicatcs and Antielides, 

 and unexpected i-elations are revealed between the 

 Vertebrata and the hivertebrata. 



In the Lepidosiren, the highest of all the fishes, we 

 find an organization of a no less complex nature. 

 This genus was founded in 1837 by Dr. Natterer for 

 the reception of a singular animal to which he gave 

 the specific name o{ paradoxa, discovered by him in 

 America, inhabiting the swamps in the vicinity of the 

 river Amazon. This species, which attains a length 

 of three feet, the body being eleven times as long as 



the head, is now becoming veiy rare. In 1839, 

 Professor Owen referred specimens from the river 

 Gambia of West Africa to the same genus, under the 

 designation of Lepidosiren annectens, and classed them 

 in a provisional group between the reptiles and fishes. 

 They are placed by Professor Pluxley in the highest 

 order of his classification of fish, namely, the Dipnoi 

 or "double breathers," and are popularly known as 

 the mud-fishes. These paradoxical "scaled sirens" 

 have well-developed reptilian lungs co-existing with 

 functional internal branchiae, and are capable of living 

 either in the water or out of it. Their structure and 

 habits are veiy peculiar. During the rainy season, 

 the waters of the Gambia overflow its banks, and the 

 mud-fish is carried out of the true bed of the river. 

 When the waters retire it is left stranded ; then, 

 burrowing in the softened mud, it coils itself up, 

 keeps open a communication with the air above its 

 nest, and breathes by means of its modified swimming 

 bladder. It thus remains inactive till the return of 

 the floods soften the walls of its cell, when it emerges- 

 and resumes its former habits. They have been 

 found in a semi-torpid state eighteen inches below the 

 surface, in situations where the ground is diy and 

 hard for months in the year, and are dug out by the 

 natives with a sharp-pointed stick and used for food. 

 A specimen of L. a7tnectens has been on exhibition in 

 the entrance-hall of the Brighton Aquarium for more 

 than two years. It is kept at a regular temperature 

 of 70 degrees, and is in a very thriving condition, 

 having grown several inches since it has been in the 

 Institution, and thickened proportionately. The 

 animal generally lies quietly at the bottom of its 

 tank, rising occasionally to the surface to take in air.. 

 It is fed three times weekly on small pieces of raw 

 beef, which it can be observed to eat in a very unusual 

 manner. When the food is thrown in the mud-fish 

 stretches itself leisurely and seizes it, as it comes 

 within reach, between its sharply-formed vomerine 

 teeth. After masticating it slowly, it throws it out 

 with a quick jerk, and, commencing at the other end, 

 repeats the manoeuvre ; it then again rejects it and 

 subjects it to a third process of mastication before 

 finally swallowing it. The body of the Lepidosiren 

 is fish-like, and covered with small cycloid scales ; 

 simply constructed pectoral and ventral limbs are 

 present, with a dorso-caudal fin. The notochord is 

 persistent, but the skull is partly bony, partly cartila- 

 ginous, and the costal arches and neural and ha:mal 

 spines are well ossified ; thus it forms a link between 

 the bony and cartilaginous types of fishes. The 

 dentition is composed of a pair of vomerine teeth, and 

 two molars in each jaw. The heart is three cham- 

 bered, and true lungs exist with rudimentary external 

 branchiae and functional internal ones. 



Among living fish, the Lepidosiren is most closely 

 related to another "dipnoid," discovered in the rivers 

 of Queensland, Australia, in 1870. This species was 

 at once, with singular accuracy, referred by Mr. 



