326 Mr Brindley, Note on Abnormalities of Dipnoan Fishes. 



arose during captivity in an aquarium, and the author has made 

 the suggestion that the branches are to be regarded as casual 

 accessory respiratory organs arising in connection with the con- 

 fined condition. 



Albrecht 1 has described a similar duplicity in the limbs of 

 Protopterus. 



Boulenger 2 , in comment of both Goeldi's and Albrecht's cases, 

 has expressed the opinion that such abnormalities arise in con- 

 nection with reproduction after injury, and with Howes has 

 described a trifid limb in Protopterus which appeared after the 

 normal limb had been nibbled by fishes in the same tank. 



Serial sections through these abnormal limbs of Lepidosiren 

 point to a similar conclusion. In them, whether the extremity is 

 bifid or not, the axial row of cartilage segments (mesomeres) is 

 present, as in Howes's Protopterus, and the appearance of the 

 cartilage cells and matrix has the usual features of young tissue — 

 the matrix is hyaline and relatively scanty and the cells are 

 actively dividing, these appearances being in clear contrast with 

 those of the cartilage of the thicker basal portion of the limb. 



Kerr has noticed that in Lepidosiren the limbs and the tail 

 appear frequently to be injured, and Budgett finds that this 

 holds good for Protopterus also. Thus in Kerr's 26 Lepidosirens 

 10 exhibited signs of regeneration of the tail, while three others 

 had bifid and probably reproduced tails. 



The radiograph shews the bifidity of the tail in one of 

 Budgett 's specimens which is on the table. 



There seems no doubt that both the limbs and tails of these 

 Dipnoan fishes have considerable liability to injury and well 

 marked power of regeneration, and also a tendency to grow in 

 a branched condition, reminding us of the cases of double repro- 

 duced tails in Lizards and Polydactyly after mutilation in Am- 

 phibians. In Lizards the extra tail is apparently sometimes a 

 growth arising from an injured place on a normal tail. 



But in some of the cases described in Lizards and in the 

 several bifid limbs of Lepidosiren which have been examined by 

 section the new growth is bifid from its commencement. The 

 existence of a tendency towards branching after injury or section 

 is well known in certain plants, but the idea presents itself that 

 an unusual expression of branching in a root or stem might 

 possibly be advantageous, while in the case of an actively moving 

 animal it would be rather an inconvenience. In any case we can 

 hardly call upon selection to account for such a tendency in a 

 vertebrate animal. As has been stated bifidity in a Lizard's tail 



1 Sitz. Akad. Berlin, 1886, p. 545, pi. vi. 



2 P. Z. S. 1891, p. 147. 



