ADDENDA. 



The following- notes were too late for insertion into the body of the 

 book : 



AMBLYSTOMA TIGRINUM Green, (p. 84). 



Don Jose M. Velasco asserts that the Siredon mexkanus {S. humholdtii) 

 undergoes a metauiorphosis, but he nowhere describes the adult. He 

 did observe in 1878* the metamorphosis of the Amblystoma tigrinum in 

 specimens from Lake Santa Isabel, three miles north of the City of 

 Mexico, It does not appear that he di'scriminates between the two 

 species, so that when he states that the S. mexicanus is found in Lake 

 Znmpango, thirty-two miles north of the City of Mexico, we are not 

 certain whether it may not be the A. tigrinum to which he refers. 



The Siredon gracilis and ^S'. liclie)ioides of Baird are both larval forms of 

 the A. tigrinum. 



Dr. R. W. Shufeldt, U. S. Army, thus describes the metamorphoses 

 of the Amblystoma tigrinum^ as observed by him at Fort Wingate, IST. 

 Mex. (Science, September, 1885, p. 2G3): 



''(1) Axolotls are more readily converted into Amblystoraas if kept 

 in water containing but little air, and vice versa. 



"(2) If transformation is forced up to a certain point in development, 

 the reptile arrives at the higher form without any further interference. 



'•(3) Axolotls live in the water with apparent comfort a considerable 

 and varying length of time after their gills have been absorbed. 



"(4) After the metamorphosis is completed their power to return to 

 the water again to live seems to depend upon the moult, and whether 

 they have lived in moist or dry places since the metamorphosis. 



"(5) By varying the conditions under which tnese animals live, we 

 can at our pleasure retard or accelerate their development to the higher 

 stages. 



"(6) Young Axolotls are more easily transformed than the older speci- 

 mens, bnt this rule also depends largely upon the conditions under 

 which these animals live. 



"There is another very im})ortant factor that enters into this meta- 

 morphosis that, so far as the previous accounts go, is not touched 

 upon, and that is the question of their diet during the experiments. 

 Axolotls are very voracious creatures and eminently carnivorous. 



* La Natnmleza, iv, 1878. 



453 



