February 5. 1903] 



NA TURB 



33i 



that .ne offspring of these specimens can easily be induced to 

 metamorphose, witness the European stock of Axolotl and 

 Amblysloma, which all have descended from the classical 

 specimens in the Jardin des Plantes. 



Velasco's important announcement that regularly metamorphos- 

 ing Amblystoma occur near the city of Mexico has become compli- 

 cated by a more recent discovery. The numerous streams of the 

 well-wooded mountain slopes which border the valley of Mexico 

 to the west and south are inhabited by A. altamirani, a species 

 very distinct from A. tigrinum. This A. altamirani metamor- 

 phoses regularly. It was described by Duges. 1 Specimens seem 

 to be very rare in collections, perhaps because nobody has taken 

 the trouble of collecting any since Duges. The types were 

 found about fifteen miles to the west of the city, at an altitude 

 of about SSoo feet, in the Monies de las Cruzes. On June 18, we 

 went by the Mexican National Railway to the station Dos Rios, 

 SSoo feet above sea-level, and fished out of the streams several 

 dozen spotted larva? of some three inches in length and several 

 adult males and females in perfect Amblystoma condition. 

 Towards the end of September, we again took some specimens 

 from the same streams. The larv:e averaged perhaps half an 

 inch more in length, otherwise there was no change visible. The 

 adult Amblystomes were still in the water, one of them a 

 beautiful, yellowish albino. On September 28, we went by the 



Fig. 1.— Chinampas or "floating" gardens of Lake Xochimilco, 

 June, 1902. 



Cuernavaca Railway to the station of Contreras, altitude 8090 feet 

 and in a bee-line about twelve miles south-south-west from the 

 city. Following up various streams, we again found the newts, 

 larva; and adult, at an altitude from 8500 feet upwards to 8800 

 feet ; further up, the rivulets were apparently too small. The 

 creatures lived in the cool, rushing stream, preferring the 

 sheltered side of large boulders, the larva; working their gills 

 vigorously, the adult motionless and never coming to the sur- 

 face ; all extremely shy and very quick. One of the specimens 

 was full of nearly ripe eggs. 



Searching in the streams only a little above the city, which 

 lies at an altitude of about 7600 feet, was fruitless. 



To return to the Axolotl, the permanent and sexually ripe 

 larva of A. tigrtnum. This is restricted to the Lakes 

 Chalco and Xochimilco, to the south and south-east of the 

 capital. No larval or adult specimens of any kind of newt 

 occur in the Lago de Texcoco, the largest of the lakes. Its 

 water is too brackish, and it was already quite undrinkable at 

 the time of the conquest, when this lake extended to and sur- 

 rounded the city. Its present mean level is six to seven feet 

 below the zero of the town, from which it is about three miles 

 distant. This lake is now silting up fast, since the marvellous 



1 La Naturaleza, 2ndser., vol. ii. (1896), 

 NO. 1736, VOL. 67] 



drainage canal not only intercepts the dangerous spates of the 

 western streams, but also drains the lake whenever its level 

 rises a few feet. However such a low rise suffices for the lake 

 to extend over many square miles of the. neighbourhood, which 

 during the dry period is covered with a white saline crust, inter- 

 spersed with scanty grass, on which cattle and horses eke out a 

 precarious existence. The lake is not quite dead; it contains 

 several kinds of fish, only one of commercial value, and numerous 

 waterfowl visit it in the late autumn. 



Lakes Chalco and Xochimilco are a paradise, situated abou 

 ten feet higher than the Texcoco Lake and separated from it by 

 several hills. High mountains slope down to the southern 

 shores, with a belt of fertile pastures, with shrubs and trees and 

 little streams, here and there with rocks and ravines. In fact, 

 there are thousands of inviting opportunities for newts to leave 

 the lake if they wanted to do so. Close to the southern end of 

 Lake Xochimilco, absolutelyclear water wells up from the bottom, 

 forming the famous ojos de agaa or springs, which are thirty to 

 forty and more feet in depth. Much of the lake, perhaps half 

 of its surface, is filled with the celebrated chinampas or " floating 

 gardens," i.e. many hundreds of islands surrounded by ever so 

 many wide and narrow canals, here and there with a large 

 stretch of water. Young little islands are still in process of 

 formation, floating masses of entangled peat, rushes, moss and 

 grass. Such floating clumps are caught, combined and anchored 

 by stakes or long saplings of willows and poplars, which are 

 driven into the muddy ground, where they soon take root. The 

 fertile mud is ladled up from the bottom, heaped upon the float, 

 which thereby is converted into an island proper, until a garden 

 is produced in which are cultivated masses of all kinds of 

 flowers, melons, pumpkins, gourds and all other produce, which 

 is taken daily to the market through the Viga Canal right into 

 the city. The larger islands are mostly surrounded by tall 

 poplars, planted in rows along the edges, thus forming a firm 

 boundary. Undue shade is prevented by lopping off the side 

 branches. None of the islands is higher than a foot or two ; 

 some are now firm enough to support houses. The depth of the 

 water averages perhaps five to ten feet, shallower towards the 

 north-west, where the lake gradually changes into a swamp of 

 rushes. The further away from the powerful springs, the muddier 

 and darker appears the water, full of suspended fresh and de- 

 composing vegetable matter, teeming with fish, larvae of insects, 

 Daphniae, worms and Axolotl. These breed at the beginning of 

 February. The native fishermen who punted us about in dug- 

 outs through this paradise knew all about them ; how the 

 clusters of eggs were fastened to the water plants, how soon 

 after the little larva; swarmed about in thousands, how fast they 

 grew, always remaining dark and never piebald or marbled with 

 yellow, until by the month of June they were all grown into big, 

 fat creatures ready for the market. Indeed, we could not get 

 any small specimens in the month of June, when we paid our 

 first visit. Later in the summer they take to the rushes, in 

 the autumn they become scarce. 



None has ever been known to leave the water or to meta- 

 morphose, in spite of Valasco's hearsay statement. But axolotes 

 sin aletas {i.e. without winglets, meaning gills) are called axolotes 

 del cerro (mountain-axolotl), or axolotes sordos (deaf, having no 

 ears). However, none of these, many of which are undoubtedly 

 A. altamirani, are found in the vicinity of the two lakes. 



The reason why there are only perennibranchiate, permanent 

 Axolotl in the lakes of Chalco and Xochimilco is obvious. The 

 constant abundance of food, stable amount of water, innumer- 

 able hiding places in the mud, under the banks, amongst the 

 reeds and roots, all these points are inducements or attractions 

 so great that the creatures remain in their paradise and conse- 

 quently retain all those larval features which are not directly 

 connected with sexual matuiity. There is nothing whatever to 

 prevent them from leaving these lakes, but there is also nothing 

 to induce them to do so. The same applies occasionally to 

 European newts, of most of which we now know instances of 

 sexually ripe " larva;." Nevertheless, in the case of our Axolotls 

 the latent tendency to metamorphose can still be revived. When 

 once sexually ripe, the Axolotl are apparently incapable of 

 changing, but that their ancestral regime is still latent in them, 

 not quite forgotten, is shown by the metamorphosing offspring 

 of Axolotl bred in Europe. 



My explanation suggested itself during our visits to these 

 lakes, which in every respect are so totally different from any 

 other lakes, pools and rivers we have seen in that wonderful 

 country. The only objection is that nobody has thought of this 

 explanation before, but I do not know of any zoologist who has 



