MAMMALIA 377 



in which the four individuals are produced from a single fertilized egg, 

 that divides at a very early period into four embryos. There is a 

 single chorion, but four separate amnia. This case is taken as evi- 

 dence that in mammals sex is determined at the time of fertilization, 

 since the four division products of a single egg are invariably of the 

 same sex. 



Extinct Edentata. The best known extinct edentates are the 

 giant ground sloths, of which Mylodon is a type, and the giant arma- 

 dillos, of which Glyptodon is the classic example. Mylodon was as 

 large and as heavy as a rhinoceros, and Glyptodon was sixteen feet 

 long. 



ORDER 7. PHOLIDOTA (SCALY ANTEATERS). This is a small order 

 formerly included within the order Edentata, but now given ordinal 

 value on account of the discovery of morphological differences more 

 fundamental than the resemblances that formerly led to 'their classifi- 

 cation as edentates. The order consists of the pangolins, which are 

 placed in the family Manidce and the genus Manis. Manis gigantea is a 

 fairly large and massive animal, about six feet in length, tail included. 

 It is native to the islands of the Malayan Archipelago. The most 

 striking feature of these animals is the scaly covering, or what ap- 

 pears to be an armor composed of large pointed, overlapping scales, 

 which are really groups of fused hairs. Scattered hairs occur between 

 these "scales." The species shown in the illustration is Manis tern- 

 minckii (Fig. 193, E). 



The pangolins are anteaters, and possess all of the characteristic 

 adaptations already mentioned for several other anteaters: the long 

 snout, sticky tongue, integumentary protection from ants, and heavy 

 claws for digging into ant galleries. Their method of capturing ants 

 is highly individual. After stirring up a colony of ants they are said 

 to erect the scales so as to allow ants to crawl under the scales. The 

 scales are then clamped down so as to hold the ants, and then the 

 animal goes in for a swim. When submerged in the water the scales 

 are lifted and the ants washed out so that they float about on the 

 surface, where they are easily picked up by means of the long tongue. 



ORDER 8. TUBULIDENTATA. This order contains only the curious 

 aard-vark, Orycteropus (Fig. 193, D) of South Africa. These curious 

 animals were formerly classed as edentates, but are now known to 

 be unique in a number of characters and have therefore been ac- 

 corded ordinal value. They are anteaters and have the slender 



