132 GEOLOGICAL SURVEY OF THE TERRITORIES. 



and the animal came more frequently to the surface of the water for air. As the change 

 went on, the dark spots increased in number and size, and gradually extended over the 

 whole upper part of the body. The membrane on the back and tail entirely disap- 

 peared, leaving in its place in the dorsal region a sharp groove. The branchiae also 

 continued to diminish, and at the same time the internal branchial arches began to 

 be absorbed, and shortly after the openings on the neck closed up. In the mean time the 

 head became more rounded above, and more oval in outline, the muzzle narrower and 

 more pointed, and the eyes more convex and prominent. The body also decreased in 

 bulk, and the costal grooves became more distinct. The thin external skin was shed, 

 and the secretion of mucus from the surface sensibly diminished. During these 

 changes the animal showed an increasing desire to leave the water, often remaining for 

 some time with its external nostrils above the surface, and occasionally making violent 

 struggles to escape. Aided by a heavy rain at night it at last succeeded, and thus put 

 an end to further observations, just at a time when it had lost the generic characters of 

 Siredon, and become a true Amblystoma, two forms of batrachians usually regarded hith- 

 erto as belonging to distinct families." 



Fortunately, a few days later, several other specimens of various sizes began, nearly 

 at the same time, to show unmistakable indications of a similar transformation, and 

 this afforded an opportunity of noting the successive phases of the change more fully, 

 as well as observing the physical conditions which seemed to promote or retard it. 

 Two of the specimens were placed in a glass jar, and left in a strong light, and five 

 others were kept in a cooler place in the shade, the temperature of the two, however, 

 differing but a few degrees. At the end of three weeks those in the glass vessel had 

 apparently completed their metamorphosis, while of the others less favorably situated 

 three only were partially altered, and at the present time, or nearly three weeks later, 

 they still retain tubercular remnants of the external branchiae, although in most other 

 respects the change appears to be complete. The two remaining specimens, however, 

 which had throughout been kept with the three last, showed no distinct signs of chang- 

 ing, although the probability of their doing so, and the importance of retaining some 

 tangible evidence of the original condition, led to the transfer of one of them to a jar 

 of alcohol after the first week, a precaution, as the result showed, quite unnecessary in 

 the case of the other, which at the time of writing (October 5) still remains a typical 

 Siredon, with no alterations more important than a single appearance in a new epi- 

 dermis. 



Similar observations had already been made by a celebrated French 

 naturalist, Professor Dumeril, on an allied species, found on the table- 

 lands of Mexico ; and it was a matter of no small interest to Professor 

 Marsh to ascertain whether this species would undergo a similar change 

 when placed under different physical conditions, hence these creatures 

 were watched with great care. 



Among the more important changes which occurred during the metamorphosis may 

 be mentioned the decrease in the size of the entire body, which was verj" marked, a 

 perceptible increase in the distinctness of the costal grooves corresponding to the ver- 

 tebrae, 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 espe- 

 cially 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 metamorphosis. 



The change in the habits of the Siredon in passing into the Amblystoma state was 

 scarcely less marked than the alteration in its physical characters. As soon as the ab- 

 sorption of the external branchiae commenced, the animal came more frequently to the 

 top of the water and took a mouthful of air ; and not long afterwards would occa- 

 sionally float for some time at an angle of about 45°, with the external nostrils above 

 the surface. Frequent efforts to leave the water soon followed, and an opportunity of 

 so doing was in most instances speedily improved, and the change then seemed to pro- 

 gress more rapidly. One or two specimens, however, showed for some time, especially 

 in cool weather, much less inclination to desert their native element, apparently suf- 

 fering little or no inconvenience from remaining under water, if allowed to come to 

 the surface about once in five minutes. The pugnacious propensities of the Siredons 

 which at first led to occasional assaults on one another, appeared to diminish as the 

 change progressed, and the more sluggish nature of salamanders at last predominated ; 

 although the altered forms at times showed no little celerity of movement, and when 

 irritated, especially when held by the tail, would often turn and snap at the hand with 

 a rapidity that would have done no discredit to a reptile of much higher organization. 



The effect on the metamorphosis of a variation in light and temperature has already 

 been alluded to. During a succession of very warm days, about the first of September, 

 the change progressed with great rapidity, but it apparently ceased, or made very slight 

 progress, in the cool week that followed. While, moreover, the two specimens most 



