408 MR. E. G, BOULENGER ON THE 



10, and 11, undei- similar conditions to those of brood 1. Nos. 6 

 and 7 were forced to breathe air, being placed in shallow water, 

 at a high temperature ; Nos. 8, 9, and 10 were placed under the 

 same conditions at a normal temperature, and ISTo. 11 was placed 

 along with No. 5 in foul water, from which the oxygen was 

 removed by the addition of boiled water. In all, therefore, I 

 had eleven specimens under artificial conditions with the object 

 of forcing the metamor]3hosis, and as a result succeeded in 

 bringing six individuals to transform into the Amblystome 

 stage, all six specimens being those induced to make free use of 

 their lungs by being placed in shallow water ; three of these were 

 kept at a temperature of between 75° and 80°, three at between 

 55° and 60". The time required for the entire metamorphosis 

 was from 12 to 16 weeks, periods which all to a remarkable degree 

 exceeded those taken by Mile, de Chauvin's specimens. Three in- 

 dividuals kept under identical conditions died in from 3| months 

 to over 5 months, but not until after having undergone a change, 

 which, although considerable, did not necessarily suggest, as will 

 be referred to later, that, but for their death, the entire metamor- 

 phosis would have taken place. The two specimens kept in deep 

 water from which the oxygen was eliminated died in the one 

 case after 19 weeks, in the other after 22 weeks. These speci- 

 mens, but for a slight reduction in the size of their gills, did not 

 undergo any change, the fins being at the time of their death as 

 well developed as at the commencement of the experiment. It 

 is worthy of note that these specimens, in spite of the fact that 

 they must have felt exceedingly uncomfortable, did not rise to 

 the surface for air, even just prior to their death, more frequently 

 than individuals kept in oxygenated water. Another point of 

 interest lies in the fact that both specimens grew rapidly during 

 this period, No. 5 from 136 mm. to 155 mm., No. 11 from 

 112 mm. to 120 mm. The specimens kept in shallow water, in 

 the case of those that died, remained stationary, while those that 

 transformed actually decreased in size. 



Text-figures 75 and 76 (pp. 406 and 407) represent eight stages 

 through which my Axolotls passed in the course of their 

 m etamorphosi s. 



Stage 1 represents the perfect larval form, the condition which 

 all eleven were in before being placed in shallow water. A few 

 days after the animals had been placed in shallow water, the gills 

 with their fringes begun to shrink, and the dorso-caudal fin 

 which lopped over to one side, to the left side in all my specimens, 

 became reduced in size, the change being plainly visible in from 

 a fortnight to three weeks (Stage 2). 



In from 10 to 20 days later the gills were only half their 

 normal size, while the fin of the back was represented by a mere 

 ridge ; that of the tail, although having undergone further reduc- 

 tion, was still well developed on the upper surface and flopped 

 over to one side ; on the lower surface, however, it showed con- 

 siderable reduction (Stage 3). It was not, however, until from 

 five to seven weeks later (Stage 4) that the metamorpliosis pi'oper 



