1574 The Zoologist — March, 1869. 



One of the most interesting features of the transformation occurred 

 in connection with the mouth of the animal. The opening, or gape, 

 increased considerably in size, one half at least: the internal and 

 external nostrils became perceptibly move distended, and the tongue, 

 which was at first small, enlarged so as nearly to cover the entire floor 

 of the mouth. An important change also took place in the teelh. In 

 the siredon the palatine series on the vomerine and pterygoid hones 

 formed an arch nearly concentric wilh the maxillary row, and ex- 

 lending forward between and beyond the inner nostrils. The arch is 

 interrupted in front, and to some extent on the sides, as represented 

 in figure la, which shows the position of these teeth, but not their 

 exact number or size. After the metamorphosis the palatine series 

 project farther from the roof of the mouth, and become much more 

 transverse, foru)ing an obtuse angle instead of an arch, with the inter- 

 spaces nearly or quite united. The maxillary series also form a some- 

 what narrower arch, corresponding to the more pointed snout of the 

 Amblystoma, and the splenial teeth of the lower jaw have gradually 

 disappeared. These changes in the dental series, it should be stated, 

 were not in all cases perfectly uniform in different individuals that had 

 apparently passed through the same external phases of transformation, 

 although the tendency was all in the same direction ; and hence it is 

 not unlikely that the palatine teeth of some, at least, of the specimens 

 examined, may eventually become still more transverse than those 

 represented in the figure. 



Among the other more important changes which occurred during 

 the metamorphosis may be mentioned the decrease in the size of the 

 entire body, which was very marked, a perceptible increase in the dis- 

 tinctness of the costal grooves corresponding to the vertebric, and the 

 gradual ossification of the carpus and tarsus. The feet also became 

 less palmate, and the toes less depressed. During the transformation, 

 moreover, and especially after its completion, all the specimens shed 

 the thin, transparent epidermis, some of them very frequently ; one, 

 indeed, which had been kept in a strong light, lost this covering 

 three times in the ten days immediately following the metamor- 

 phosis. 



The change in the habits of the siredon in passing into the Ambly- 

 stoma state was scarcely less marked than the alteration in its physical 

 characters. As soon as the absorption of the external branchiae com- 

 menced the animal came more frequently to the top of the water and 

 took in a mouthful of air; and not long afterwards would occasionally 



