The Transformation of the Mexican A xolotl. 625 



is quite rudimentary. Whilst in the Salaman- 

 drina the capacious intermaxillary cavity is en- 

 tirely filled by the tubes of the gland in question, 

 in Axolotl this cavity is almost completely filled 

 with a closely woven connective tissue, in which 

 there can only be found a small number of gland- 

 tubes in the extreme front, and at the base im- 

 mediately over the intermaxillary teeth these 

 tubes agreeing in the details of their histological 

 structure with the elements of the same gland 

 in the Salamandrida. 



I give these anatomical details from Dr. 

 Wiedersheim's verbal communication. An ampli- 

 fied account will subsequently appear in another 

 place. 84 



An explanation of this rudimentary intermaxillary 

 gland in the Axolotl only appears to me possible 

 on the supposition that the latter is an atavistic 

 form. From this point of view it is evident that 

 the gland already present in all Amblystoma-\ax\i. 

 must have been taken over by the perenni- 

 branchiate form of the existing Axolotl, through 

 the reversion of the hypothetical Amblystoma 

 Mexicanum of the " diluvial period." 4 It can 

 also be easily understood that this organ would 

 become more and more rudimentary in the course 

 of time, since it has no further use in the water, 



* [Eng. ed. See this author's work, " Das Kopfskelet der 

 Urodelen." Leipzig, 1877, p. 149.] 

 " [See preceding note 52. R.M.] 



