THE SPINOUS PROCESSES m 



of the disposition of the spinous processes. In this 

 feature the majority of them follow the Tree Shrews, 

 and those that are characterized by special activity 

 present a remarkably double-sloped series of spines. 

 Some Lemurs might almost be called arboreal jumpers, 

 and among them the Bornean Tarsius and the African 

 Galagos are most prominent; in these animals the forward 

 slope of the lumbar spines is particularly acute. But 

 with some other Lemurs the most puzzling feature of the 

 problem is introduced, for Nycticebus, as a type of the 

 Asiatic Slow Lemurs, presents a series of spines as uni- 

 formly retroverted as that seen in the Sloths themselves. 

 Some confusion between the Sloths and Slow Lemurs 

 has, in bygone days, been a stumbling-block in systematic 

 zoology. Is this similiarity of the backbone another 

 feature which might cause the animals to be confounded 

 and is it one that might point to any real philogenetic 

 affinity in the stocks of the Slow Lemurs and the Sloths ? 

 In this feature we have seen some reason for believing 

 that Sloths were derived from a lumbering terrestrial 

 stock, and it may fairly be asked if the same reasoning 

 should not apply to the case of Nycticebus. "We have 

 pictured the stock of the Lemurs as arising most probal)]y 

 from a small active animal; are we to regard the Slow 

 Lemurs as having a different origin ? 



Probably the correct answer is that the Slow Lemurs 

 show so many points of affinity with the rest of the 

 Lemurs that they can only be regarded as altered members 

 of the same stock. " Although they vary considerably in 

 structure from the more typical Lemurs, there can l)e 

 no doubt that the Slow Lemurs possess a true Lemurine 

 structure in many important particulars, so tlial they 

 must have had a common origin with the true Lenuirs " 

 (Sclater). We are bound, therefore, by our ]>rcsrnt 

 limitations of knowledge to regard this as a case of con- 

 vergence. We have previously noted the peculiarities 

 of the arboreal habits of Nycticebus. It is a trce-clinger 



