670 MAMMALIA [CH. 



uncovered. In many cases there is a shallow cloaca surrounded by 

 a sphincter into which both anus and urino-genital passage open. 

 They possess an allantoic placenta, but this covers only a portion 

 of the surface of the egg, the rest of the surface of the egg being 

 occupied by an umbilical placenta. In this respect they are hardly 

 more advanced than those Metatheria which retain an allantoic 

 placenta. The Insectivora, as may be seen from the description, 

 are a very primitive group, and like other primitive groups consist 

 of a number of families widely differing from one another in struc- 

 ture. Taking a broad view we may say that the tropical families 

 exhibit the highest grade of structure. Thus the GALEOPITHECIDAE, 

 or Flying-shrews, represented by the genus Galeopithecus, have a 

 parachute-like expansion of skin extending from neck to hand, 

 forming a web including the fingers. A similar expansion of skin 

 reaches from wrist to foot, forming a web between the toes, and 

 there is a piece of skin connecting the two legs behind. There is 

 a ring of bone round the orbit, and the symphysis pubis is long and 

 strong. The TUPAIIDAE, or Tree-shrews, have likewise the orbit 

 encircled by bone and a strong symphysis pubis, but they are devoid 

 of any parachute-like extension of skin. They are small animals 

 with large eyes and long furry tails ; both these groups are confined 

 to the Malay Archipelago and India and both inhabit trees. 



The MACROSCELIDAE have no bony ring round the orbit but they 

 possess a strong symphysis pubis. Their most marked characteristic 

 is an elongated foot (see Fig. 336) which enables them to make great 

 springs. Hence the name Jumping-shrews. They are represented 

 by 14 species distributed over Africa. 



The three families which represent the Insectivora in Great 

 Britain are all of a lower type. Not only is the orbit never 

 surrounded by bone but the zygomatic arch is slender and sometimes 

 even absent. The brain cavity is very small and the symphysis pubis 

 is very short ; sometimes the pubes are united only by ligament. 



The first of these families is the ERINACEIDAE, or Hedgehogs, 

 distinguished by the slender zygomatic arch, and by the tympanic 

 being in the form of a ring. The well-known Hedgehog, Erinaceus 

 europaeus, is intermediate in size between a rat and a rabbit. It has 

 the fur intermixed with spines, and when alarmed can roll itself 

 into a ball, tucking in head, limbs and tail, and in this condition can 

 bid defiance to its enemies. All Erinaceidae are not of this character; 

 the rat-like Gymnura from India and the Malay Peninsula is 

 without spines. 



