Ko. 486] HABITS OF AMBLYSTOMA 



water represents an advance upon the habit of external fertihza- 

 tion, and a stage in the evolution of habits that are to make possible 

 the invasion and permanent occupation of the land. 



Internal fertilization also finds a biological significance in the 

 fact that in the course of its development there is gradually effected 

 an economy in the amount of seminal fluid required for fertiliza- 

 tion. This factor may account for the persistent development of 

 the habit under aquatic conditions, where external fertilization 

 is still possible; the incidental result is a preparation for terrestrial 

 life. 



In existing Amphibia we may find illustrations of various stages 

 in this evolution of the breeding habits correlated with a transition 

 from the water to the land. In Cryptobranchus, one of the lowest 

 of the Urodela, leading an aquatic life and showing only in its 

 methods of respiration and locomotion an advance to\\'ard terres- 

 trial conditions, external fertilization takes place. This is evi- 

 dently the primitive condition for the Urodela. In Amblystoma, 

 a urodele living partly upon the land but returning to the water 

 to breed, we see developed the peculiar habit of fertilization by 

 means of sperm atophores — a mode of internal fertilization favored 

 by aquatic conditions. In Triton viridrsrrns an economy of 

 seminal fluid tiirough a reduction in the nuinl)cr of sperm;itoi)h(>re.s 



Savi., Molgc a.spcra Duges and GlossoUga lla(jcnLdlvn Latastc. 

 according to Bedriaga ( '82 and '95) the male emits spcruiatopliores 

 while still clasping the female; in Triton iorosus Escli. (Ritter '99) 

 it is probable that a very similar process occurs; in none of these 

 cases, with the possible exception of Molge aspera, is there direct 

 cloacal contact. Finally in the Apoda (the Sarasins '87-'93; 

 Brauer '97) we find the establishment of a method of internal 

 fertilization bv direct c-loacal contact, thus fulfilling the require- 

 ments for continnons residence ii})on the land. 



