356 



sideofthebody between the thigh of the normal leg and the trunk. 

 Attached to the distal end of this stalk is a broad undivided definitely- 

 shaped plate [D), which represents the fused aborted thighs of the two 

 additional legs. This plate is rounded in front and posteriorly bears 

 the two crura. The greater part of the crura and the remainder of the 

 two additional legs are normal in every respect. Thus it will be seen 

 that during metamorphosis the additional legs have been twisted round 

 from the left side through a considerable angle, having originally been 

 situated one on either side of the normal leg. This change of position 

 was due to the production of the stalk, which not only resulted in the 

 ^egs assuming the posterior position but also did away with the muscular 

 connection between the legs and the body which at first existed; in 

 other words, the legs, after the formation of the stalk, were merely 

 dragged about by the animal and were indeed rather an incumbrance 

 in its movements. The legs were quite healthy in appearance (though 

 somewhat anaemic just after the metamorphosis), the skin being pig- 

 mented and the muscles well formed; also they were quite as sensitive 

 to mechanical stimulation as the normal limbs. In fig. 2 is represented 

 the normal j)osition of the limbs — the position assumed when the frog 

 was swimming e. g. In this position the plantar surface of the feet 

 was uppermost, the post-axial aspect of the limbs being anterior; in 

 other words, the limbs, in their normal position were upside down 

 (see remarks above on the same condition found in the tadpole). How- 

 ever, the stalk being very flexible, the limbs were often rotated into 

 the opposite position and indeed into almost any position, and I have 

 occasionally seen them accidentally thrown over the frog's back when 

 the animal was active. 



One other noteworthy fact is that this abnormal frog was further 

 abnormal in that it was quite twice the size of any other young frog of 

 the same age (about five weeks) and much lighter in colour. At the 

 time when it was killed, the trunk (from tip of snout to posterior end) 

 measured 14 mm in length, whereas other frogs of the same age only 

 measured about 10 mm and were markedly smaller in every way. 



In transverse section the stalk bearing the legs proved to consist 

 merely of the normal integument, a dense central mass of tissue formed 

 of closely-packed cells, several small blood vessels and a small amount of 

 muscular tissue. 



As regards the skeleton of the additional limbs, the distal cartilages 

 were quite normal, but the tibio-fibula of each hmb, normal on the 

 whole, disappeared for a certain length in the upper part of the crus, 

 and only reappeared just before its insertion into and fusion with the 

 mass of cartilage which composed the plate D. The cartilage of the 



