In concluding I may mention an anatomical fact which most strongly supports my view that the Mexican Axolotl is a reverted Amblystoma. I learn from Dr. Wiedersheim that the Axolotl possesses the “intermaxillary gland” which occurs in all the land Amphibia. This organ, lying in the intermaxillary cavity, appears, whenever it occurs, to produce a kind of birdlime, _i.e._ a very glutinous secretion, which serves to attach the prey to the rapidly protrusible tongue. Although this secretion may perhaps also have another function, from the absence of the intermaxillary gland in all exclusively aquatic Amphibia, it follows that it must be devoid of importance for, and inapplicable to feeding in the water. The intermaxillary gland is absent in all _Perennibranchiata_ and _Derotremata_ which Wiedersheim has hitherto investigated, viz. in _Menobranchus_, _Proteus_, _Siren_, _Cryptobranchus_, _Amphiuma_, and _Menopoma_, all of which are indeed without the cavity in which the gland is situated in the _Salamandrina_, _i.e._ the _cavum intermaxillare_. Now in the _Salamandrina_ the gland appears at an early stage. It is possessed in a well-developed state by the larvæ both of species of _Triton_ and of _Amblystoma_, where indeed the glandular structure completely fills the _cavum intermaxillare_. Were the Axolotl a species retarded in phyletic development, the presence of a gland which does not occur in any other _Perennibranchiata_, and which is only of use for life upon land, would be quite inexplicable. The matter becomes still more enigmatical through the fact that the gland, although present, is quite rudimentary. Whilst in the _Salamandrina_ the capacious intermaxillary cavity is entirely 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 immediately over the intermaxillary teeth--these tubes agreeing in the details of their histological structure with the elements of the same gland in the _Salamandridæ_. I give these anatomical details from Dr. Wiedersheim’s verbal communication. An amplified account will subsequently appear in another place.[278] 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_-larvæ must have been taken over by the perennibranchiate form of the existing Axolotl, through the reversion of the hypothetical _Amblystoma Mexicanum_ of the “diluvial period.”[279] 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, and the gap thus arising in the formerly present _cavum intermaxillare_ would become filled with connective tissue.