METAMORPHOSIS OF THE AXOLOTL. 409 



took place, when the part of the dorsal fin nearest to the head 

 began to be entii-ely absorbed ; at the same time the head became 

 shorter, assuming a more Salamander-like shape, Avhile a swelling 

 above the eye foreshadowed the advent of the upper eyelid ; the 

 gills at this stage measured but from 3 to 5 mm. ; the fin of the 

 upper edge of the tail, although now much reduced, still lopped 

 over to one side ; the lower fin, but for a rudiment at the extreme 

 end, had entirely disappeared. 



Stage represents the conditions seven to eight days later, 

 when the dorsal fin had retreated to the middle of the back ; 

 the caudal fin on the lower surface had entirely disappeared ; the 

 head had quite altered in aspect, having become much shortei', 

 giving the eyes the impression of having been shifted forwards. 

 At this stage the upper eyelid had become completely formed, 

 the lower eyelid being incomplete. 



In from seven to nine days later (Stage 6), the fin of the back 

 had receded to a level with the hind limbs, while on the upper 

 surface of the tail, where it still lopped over, it measured only 

 1 mm. Both eyelids were now formed. At this stage the 

 animals raised their heads completely out of the water, and 

 the opportunities they were given of getting on land were 

 taken advantage of. Stage 7 represents the creatures about a 

 week later, when nothing remained of the fin but a mere rudi- 

 ment bordering the extreme end of the upper surface of the 

 tail. The gills were represented by three knobs. Stage 8, the 

 perfect form, the gill slits having closed up and the tail having 

 become more or less roundish, was attained five to eight days 

 later. In the case of both Dumeril's and Mile, de Chauvin's 

 specimens the yellow spots appeared several days prior to the 

 complete metamorphosis ; in all my specimens, however, it was 

 not until after they had attained the perfect Amblystome con- 

 dition that the yellow spots put in an appearance, these being 

 situated on the sides of the body, tail, limbs, and throat ; none 

 appeared on the back. 



As I was desirous of ascertaining whether the metamorphosis 

 could be checked and the shrinking gills and fins made to undergo 

 fresh development, and if so, at what stage it could no longer be 

 checked, two specimens were taken out of the shallow water and 

 replaced in deep water as they reached successive stages in their 

 development. Ko. 6 was kept at a temperature of between 75° and 

 80°, and No. 9 at a temperature of between 55° and 60°. Both 

 these Axolotls were placed in shallow water and then induced to 

 breathe air frequently by means of their lungs on October 7th, 

 Stage 2 was reached on October 20th ; they were then replaced 

 in deep water. The gills grew immediately and the fins developed, 

 Stage 1 being reached again on October 28th and November 5th. 

 They were then once more put into shallow vessels, with the 

 result that the gills and fii:is again began to shrink, Stage 2 being 

 attained on November 15th and 20th, Stage 3 on December 5th 

 and 26th. On the latter dates they were again transferred to 

 deep water, St:ige 2 being attained on December 20th and 

 January 10th. The metamorphosis was continued on placing the 



