134 MAMMALIAN DESCENT. [Lect. V. 



matoiis, types on tlie other. It is hard to say what their 

 own diagnostic marks are, for they are evidently not 

 hardened into a fixed zoological group, but are, as it 

 were, a collection of plastic types ; low, as having the 

 stigma of ancientness upon them, and yet full of the 

 promise of all that is highest in the great mammalian 

 Class. 



In all this group, only one type, the large aquatic otter- 

 like Potamogale of West Africa, is devoid of clavicles ; 

 also the presence of five fingers and five toes is very 

 constant ; the pollex is deficient in Rhynchocijon and one 

 species of Oryzorictes, and the hallux in MacrosceUdes 

 tetradactylus. Five is evidently a sacred number to 

 nature ; the Amphibians — Salamanders and Frogs — 

 usher in this fixed number, fixed as against a greater 

 number ; and man rejoices in its retention in his own 

 hands and feet. That which often characterises a 

 declining dynasty is the dwarfed condition of its 

 members, as well as the loss of certain of its families ; in 

 the past history of the types it is generally written 

 down that "there were giants in those days." In 

 minuteness, one of our native Shrews is the rival of 

 that smallest Bat, the Pipistrelle, and that smallest of 

 the Eodents, our beautiful scjuirrel-like Harvest Mouse. 

 These three types of Mammalia show us how small a 

 vessel of life will hold all that is essential to one of 

 our own class ; these nursino- mothers are no lars^er than 

 some of the insect tribes. Here we see that, as the lowly 



