CHAPTER XXI 



THE REPRODUCTIVE SYSTEM 



THE influences of tree-climbing upon the reproductive 

 habits, and consequently upon the reproductive system, 

 are very great. They may be considered under two 

 headings : as due to the arboreal life alone, or as they are 

 outcomes of the emancipation of the fore-limb, which is 

 itself a consequence of the arboreal life. The great factor 

 involved under the first heading is the necessity for the 

 reduction of the family in arboreal life. Arboreal animals 

 tend to have small families, and some of the influences 

 which have brought about this result are perfectly obvious. 

 In the first place, large litters are, as a rule, produced 

 among animals living such a life as affords rest and 

 protection for the female during pregnancy. Pregnancy 

 with a large litter and active arboreal life are almost 

 incompatible. No matter what the underlying regulating 

 factor may be, it is quite definitely in action, and although 

 nest-building may offer a temporary expedient in a race 

 of arboreal animals, reduction in the number of offspring 

 produced at a birth will be the ultimate result. Again, 

 apart altogether from the disabilities of pregnancy, there 

 are the difficulties of dealing with large families when 

 born to an arboreal mother. Helpless offspring in large 

 numbers may be managed and cared for in some safe 

 terrestrial nursery, but up a tree even were large numbers 

 of such offspring produced, it is doubtful if many would 

 survive. We know that the Tree Shrews build a nest, 

 and so do some of the Lemurs (Cheirogaleus), as well as 

 arboreal animals of other stocks, such as Rodents 

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