822 THE POPULAR SCIENCE MONTHLY. 



should they be called prosimians, or should they figure among 

 the primates ? 



The primates might be well defined by saying that they are 

 placentary mammalia, non-aquatic — which excludes the cetaceans, 

 sirens, and pinnipeds ; without hoofs — which excludes the ungu- 

 lates and j)roboscidians ; having three kinds of teeth — which re- 

 moves the rodents and edentata ; and having molars neither with 

 cutting blades nor with sharp, conical points — which excludes 

 the carnivora and insectivora. They have no absolutely peculiar 

 characters in common, naturalists not regarding the type of the 

 cerebral circumvolutions. They have a discoidal placenta, and a 

 uterus with a cavity not two-horned ; the cheiroptera or bats have 

 likewise the third characteristic. They have two pectoral mam- 

 mae ; but so have the bats and the lamantins. 



The teeth vary among them as to number, form, and perma- 

 nence. They appear more specialized, brought nearer to one an- 

 other, and more fixed in their general form, as we ascend toward 

 man. There are four stages in the last category — the lemurs, the 

 monkeys of the old continent, the monkeys of the new continent, 

 and man. 



The replacement of claws by nails forms one of the most im- 

 portant characteristics of the primates. Claws are designed and 

 formed for attack and defense ; the hoofs of the ungulates form 

 hard soles for the feet, protecting them from contact with the 

 ground and facilitating the march of the animal ; while the nails 

 are so shaped as to be adapted to the purpose of prehension. 

 This adaptation is more or less perfect, and extends to more or 

 fewer fingers among the primates, permitting another division 

 into the perfect primates, like man and all the monkeys but one 

 group, and imperfect primates. Another adaptive characteristic, 

 the corollary of the nails, is the well-developed thumb, removed 

 from the other fingers, and opposable to them. More completely 

 than they, it also indicates an organ made to clasp, to seize. The 

 primates may also be divided by this feature into three groups 

 Man, with whom the thumb is opposable only on the fore-limbs 

 the monkeys, with which it is opposable on all four of the limbs 

 and the imperfect primates, with which the adaptation is less exact 

 or less marked on the hinder than on the fore limbs. Other char- 

 acteristics, usually graduated in the ascending series of the pri- 

 mates, might be mentioned ; but these are enough for our purpose. 



To regard the primates in this way is a little to prejudge the 

 solution we are seeking. From the instant we suppose a pro- 

 gressive development of characteristics in the series and divide 

 the primates into superior, medium, and inferior, we are tempted 

 to be indulgent in respect to characteristics which may be little 

 accentuated or wanting in the last. From this, to assuming that 



