6 ARKIV FÖR ZOOLOGI. BAND 12. N:0 13. 



m^ is missing on both sides in one of the skulls. This tooth 

 is of course always small, and more or less useless as it sits 

 so far back that is bas no antagonist to work against. It 

 is thus almost to be dassed araong tbe rudiments and is 

 subjected to tbe variability of sucb organs. 



As a summary of tbe discussion above it may be said 

 tbat tbe lycoides skull in several, or most respects is not only 

 larger tban tbe magellanicus skull, but it represents at tbe 

 same time in several respects a more advanced stage of 

 development. Tbis is a very interesting fact, but it is ratber 

 difficult to find out wbicb circumstances possibly bave caused 

 tbis increase in size and furtber development of tbe Pseiid- 

 alopex on tbe soutbern side of tbe Straits of Magellan. 



Tbe tbeory bas been advanced^, tbat a colder climate 

 is apt to produce a greater bulk of the warmblooded animals 

 tban a warmer climate, because it is easier for tbe larger 

 animals to retain tbeir temperature witb tbeir comparatively 

 to tbeir size smaller exposed surface. Even if tbis may bave 

 application in some instances, tbe exceptions are too numer- 

 ous to make tbis tbeory a general rule, at the same time 

 as it must be remembered tbat tbe warmblooded animals may 

 be sufficiently protected by fur, featbers, fat etc. to endure 

 tbe climatic difficulties if otber conditions of life are filled. 

 In tbis case the climatic differences hardly can be considered 

 sufficient to cause tbe different size of tbe Pseudalopex forms 

 from the opposite sides of the Straits of Magellan. Abund- 

 ance of suitable food is probably more often apt to increase 

 the size of the animals tban anything else. To judge from 

 descriptions there may certainly be plenty of food for the 

 Pseudalopex of Tierra del Fuego in the shape of Tucotucos, 

 Guanacos, numerous seabirds and so on. But on the mainland 

 as well food ought not to be lacking. There is one notable 

 difference in tbe fauna north of the Straits, viz. that the 

 Puma lives there, whereas to the south of the Straits Pseud- 

 alopex lycoides is without competitors, being the largest and 

 only carnivorous animal there. Perhaps this may account 

 for something, although it hardly can serve as explanation 

 for the greater size of the Tierra del Fuego form of Pseud- 

 alopex, Tbis Pseudalopex must, no doubt, be a ratber 



^ By K. Berqmann 1849, and Hans von Boetticher (Zool. Jahrb. 

 40) 1917. 



